Not sure I (37M) can take it anymore

I think I need some help. I have two daughters, 4 and 7. My wife and I have been together 19 years and married for 11.My daughters are incredibly challenging to parent. They cause me an unending amount of stress and anxiety which tends to result in me losing my temper with them often. They are one of the reasons I already take antidepressants.My wife and I are sure that my eldest (A) has mild autism of some kind, which presents as a constant unwillingness to do what we ask or tell her to do, and with some strong obsessive compulsions (e.g. only having a few different pairs of underwear or dresses she will wear, foods that have to be prepared and presented in a certain way etc). She has screaming fits and huge meltdowns if we try to do anything that is outside of her comfort zone. We don't have a medical diagnosis but are planning to get one.My younger daughter (B) probably doesn't have the same condition but has started to mimic her older sibling. The two of them fight. Constantly. Bitterly. They bicker, hit and pull hair.We agreed from the start to be gentle parents. We don't do punishments, time outs etc. Obviously we do not smack. But A's behavioural traits have gotten so much more challenging and now I feel like I don't know how to parent her to ensure her health, wellbeing and safety anymore. When she is behaving in a way that is unsafe or inappropriate or inconsiderate, I feel like I have no way to get her to stop. Shouting or raising my voice doesn't work. Gentle reasoning and pleading has lost any impact. If I say anything negative her response varies from: blowing in my face, saying 'you are a poo', screaming in my face, running off to mum saying 'daddy shouted', or more recently, hitting me. Distraction often works e.g. giving her my phone or something to watch on TV but I can't keep doing that, else I fear we will just be stuck in a rut of her glued to a screen and never doing anything.I love them both so dearly. But it is affecting my mental health and I feel that I can't be a good father to them anymore. I get so frustrated that I have to walk away when she is behaving in a challenging way. That just places extra burden on my wife and causes us to argue more. I can't abide being hit by my daughter even though I know it's not something that she has full control of. But I feel like a terrible father just walking away.Any advice would be so welcome right now. TIA.TL;DR: two daughters, eldest highly likely ASD and exhibits v. challenging behaviour inc violence towards dad. Dad is losing faith in his ability to parent. via /r/Parenting https://ift.tt/2yi81In