Not sure whether to believe 7 year old or not.

Hi r/Parenting,I'm stuck in a tricky situation here and thought I'd get some opinions.I have a 2 yr old and a 7yr old. It's been a year and a half since their father and I split and went through a very nasty divorce, which has ended up with 50/50 custody.Their father and I do not get along and only communicate about the children and nothing more. I have no idea where the kids are when he has them, what they do, who they see. I basically don't know half of my kids lives. This has left me with guilt and anger with the situation. The oldest unfortunately detects the hostility though I try my best not to allow anything on my end from her seeing that. I do my best not to try "winning" my kids over for the sake of my own feelings towards their Dad.When asking my two year old about a bruise on her chin last night, she said "Daddy did it". When changing her today, I noticed another bruise on her leg and asked again where she got the booboo and again she's said Daddy.So I went out to my 7 yr old and said "I don't know why your sister keeps saying her booboos are from your Dad. That's not true, right? Your father doesn't hit your sister I hope?"My 7 yr old responded:"Well, he hits her when she's being bad. Jane(exHusbands fiancé, name changed)and Daddy sometimes hold her arms down and smack her face and scream at her to stop. And they push me out of the room so I can't see. And he smacks her butt really hard. "I don't want to assume worst case with this, so I calmly asked what else goes on without trying to have her make stuff up by being too aggressive with the questions.And she told me that Daddy screams at her sister a lot and tells her to shut up. And he gets so mad that he'll throw stuff.My exHusband was abusive with me and we argued a lot about how hard he disciplined the oldest when we were together. What my daughter has told me is putting a fear in me I haven't felt since we split, but I think I am fearful of my daughters wellbeing. She is definitely a handful, while her sister was a very calm toddler.My ex is also expecting a new child with his fiancé and I'm worried that the stress my two year old puts on him might flip a switch in him that may cause him to snap - especially because of his animosity towards me.Based on what my daughter has told me I'm wondering if children and youth should be contacted or if it might be my daughter over exaggerating how he disciplines her and my own feelings maybe getting in the way.I'd really like some advice. I'm afraid if I contact C&Y they'll think this is just a tactic for me to try and get custody of the kids, but I'm also afraid if something is going on and no one detects or does anything that my daughter is going to be a victim. I just don't know where to go from here. via /r/Parenting http://ift.tt/2eHkZ9V