Is this behaviour starting to get out of hand?

My niece and nephew are 2 and 4 years old. I am very close to my sister/their mum. I used to go round and see them at least once a week but ever since she broke up with their deadbeat dad about 7 months ago, I have been at her house nearly every day (spending whole days, whole nights, sometimes a whole 3 weeks). My point being that I am around them a lot and see basically every aspect of their life from the moment they wake up to when they go to sleep. I've always done things for them from the moment they were born, that most people would maybe consider a lot coming from their uncle. And I know I might come across as someone who is just sticking their nose in, and that I'm "just the uncle". I know those kids aren't mine, but they're as good as. Its basically now me and my sister raising those kids now (although sometimes it feels like its more me). Ever since my sister broke up with their dad I seem to have taken on that role, accidentally.I get them up, dress them, feed them, take them to nursery, bath them, play with them, talk to them, teach them stuff, bake cakes, dig in the garden, build towers, pick them up when they fall over, put them to bed, tuck them back into bed when they get out in the middle of the night. While at the same time doing chores around the house. At first I just wanted to help and support her, to show her she is not alone with these two children. But it seems that now she has come to expect all of this from me. When I am there (which is a lot) she sees it as the perfect opportunity to sit on her phone. Part of me feels that because of how the children behave she wants a break, and because I am there she knows the kids will be looked after. Now these kids are in NO way shape or form neglected, I just think that over these past few months they have really defeated her with the behaviour that has been going on. I understand at the end of the day they are just kids. Everything is a learning curve for them. But I starting to worry that this is turning into more that just "terrible two's" and childish horseplay.The 4yo basically runs the household if i am not there. My sister spends her day tip-toeing around him, trying to prevent a meltdown. He doesn't ask, he demands. When he speaks it's either in a whiny tone, or a "I'm telling you" tone. Even with constant prompting you never hear "please/thank you". He'll pee on the floor on purpose, he'll try to hurt or harass the cats, he'll hit his sister and tell her to do naughty things (which I get is rather common in siblings but recently the things he has been telling her to do have got more and more extreme). He'll only break things that he knows isn't his. You can ask him to do something simple like "Please can you go and get your shoes, we are going out in a minute." and it will be met by staring off into the distance pretending that he did not hear you (but you know for sure you did have his attention), "no/why?/you get it/ *cries*". We can't go shopping without him having a massive meltdown with kicking, hitting, and screaming to the point of getting hysterical. Before this happens we have tried to get him involved in the shopping to try and give him something to do/focus on, but this only works for about 5 minutes before he'll start up over seemingly nothing. Once he has started there is no going back LOL. My sister at this point tries to ask him questions about what he "wants to do?". I tell her he doesn't know what he wants right now, so we either have to try and control him or go home. She just kinda gives me a baffled look, like she's surprised that I wont allow him to behave like that in a shop. His general attitude towards people has really changed. And I know it seems obvious "well his mum isn't with his dad anymore" but these kids are actually much happier without him, they were scared of him and he wasn't exactly a good role model for them. His sister (the 2yo) is similar, just a more toned down version. But she seems to be heading the same way.I'll never spank them, simply because they are not my kids. Although I come from a family where if you really overstepped the line you got a swipe round the back of the head or on the bum. I was never beaten or hit excessively, but when it happend boy you knew you had fucked up. You took a good hard look at yourself. I honestly do think that I helped shape me into somebody who understands why there has to be rules, boundaries and respect for others (especially for those who look after you). I try the naughty step, I try taking a toy away, I try taking treats away (not all at the same time), I try to have heart to heart talks to try and understand where this is all coming from. But the trouble is, my sister doesn't back me up.She could sit there and see the bad behaviour happening in front of her, will see me trying to correct them, but do or say nothing. The children have learnt that if they cry and run to her, she will comfort them.I'm starting to think I am crazy for even thinking this now but in my head: Taking on parental responsibilities in most aspects (as i stated before) = Support/back up in other aspects.I was wrong apparently. I've bought them sticker charts, my sister lets them destroy them. I have wrote letters to them pretending to be "The Food Fairy" in an attempt to get them to eat something other that chicken nuggets and chips, but my sister just didn't seem to care/didn't get behind it. I've tried waking them up with an extremely positive enthusiastic attitude, trying to make the most mundane things like getting dressed "awesome!", throwing in loads of "well done!/Good job!/ I am so proud of you!", but it's like he can sense you are trying and after a few minutes he will instantly become moody, he'll try to upset his sister if he can see she is having fun with it. But that's what I don't understand, he most definitely is not left out (therefore would try to ruin his sisters fun because he feels he's not having any). If anything most of it is aimed at him.It's weird because me and my sister are close enough that we both have a mutual understanding that it is alright for me to address the kids behaviour, but at the same time she doesn't help/doesn't seem to bother with punishment or reward schemes. Therefore the kids run to her and everything i have said/done/tried to do gets unravelled. The only time she will say something is if one of them touches her phone. The have broken around 8 phones in the past year.I know it doesn't really sound like it from this post, but I really do love all of them. Like I said before, they have basically become my kids. And I am not a power-crazy person who throws their weight around. I understand they are kids, but we seem to be going backwards instead of forwards when it comes to behaviour development. I'm just really worried that they are going to land themselves in some serious trouble later on in life. And that I will be just "another wasted life" when if someone had just stepped in a bit sooner it could have gone differently. My sister seems to think that "school will sort out" the 4yo, but I don't want this to be left to chance- "oh they will probably grow out of it". They both go to nursery just now and the teachers say they have absolutely no problems with them. So it's just a problem at home.My sister once suggested that the 4yo might have some form of "behaviour issues/problem" like ADHD/ADD. Now, I am in no way an expert, and I could be completely wrong and I apologise for my ignorance if I am. But the fact that he (the 4yo) behaves perfectly at nursery suggests to me he doesn't have such issues. I'm just going off "if he had something he wouldn't be able to control where and when it makes itself present", the fact that he old plays up at home makes me feel its more about being naughty for the sake of it. Although, I could be completely wrong.Like I said, I really think this is starting to turn into something more than childish horseplay. Words to not really begin to shine a light on just how bad the meltdowns are, the daily behaviour, or the level of attitude this 4yo has is rather shocking. It's strange because he has never really been exposed to language/behaviour like that. His dad wasn't a very nice person, but his behaviour was more aimed at their mum/my sister when the children were not around. I know that kids are great at sensing when something is up, but the real "woah you need to calm down/where did you even hear that?" attitude has only made itself know in the past 3 months. Could he still be influenced by something he possibly saw over 7 months ago? And would it still take this long to come out? Or is it something unrelated?Is there any way I could talk to my sister about this without sounding too harsh, but at the same time let her know how serious I am/how serious this could be? Any tips/tricks? Non-physical punishment ideas for when the "conventional" ones seem to stop working? Am I doing something wrong here? Could I do anything differently? Is there more effective ways of talking/getting it through to a child that this type of behaviour cannot go on? I really do love them with all my heart but it is starting to make me not want to go round anymore. Which is a shame because I love going to see my sister, we've been there for each other through thick and thin.It sounds dramatic but I also have a heart condition, and recently with all the shenanigans going on/my sister not helping I feel like I could keel over from the stress LOL. And I say this again because I really really do mean it, I love them all. I just want the best for them. Thank you :) via /r/Parenting https://ift.tt/2szBnhT