They spend 2 nights a week there which, aside from anything else, I really need because I work f/t and have to bring work home and go in early as well.
I have had many concerns over the 4 years we've been apart, such as his house being dirty, the unlimited screen time they get there and the lack of discipline/chores he enforces. I realise (and have been told on here) none of that is my business. However, for the last year or so ds1(10) has been increasingly reluctant to go there and especially complains when he has to go there for longer periods in the holidays.
More recently he has complained more vociferously about it and has started saying he hates his dad and that his dad is biased towards ds2. Now he accuse me of similar and can be quite negative and moany when he gets going anyway, but I started to feel I needed to address it. My feeling is ds2 is incredibly stubborn and wilful and ds1 is an appeaser. I try very hard when they're with me to challenge these roles and tell ds1 he's not responsible for ds2 or for stopping arguments in the house (he'll tell me to give in to ds2, and if the issue is related to him, such as when d2 kicks off when it's time for them to swap turns on the xbox, and he can sense me getting annoyed for example). However, I am firm with ds1 when he hits ds2 - they have been annoyingly physical with each other from as soon as ds2 could move really). From what ds says, ex gives in to ds2 pretty much all the time. I imagine he does this for an easy life and because he is lazy and hasn't put time and effort into thinking about how to handle them - they're not easy!
Now yesterday he has told me ex hits him when he hits ds2. There are no marks on him but he says it hurts and is scary 
. He says dad shouts a lot and I said 'worse than me?' - I will admit to being a shouty parent at times but have worked very hard to calm it down, with some success. He said dad probably shouts less but quite a bit and it's scary when he does. He says mine isn't scary. Ds2 didn't say 'no he doesn't hit you liar' - not that I think ds1 is a liar of course. It's just I know he doesn't like going there. I can't seem to ascertain whether this has happened just once or twice (not that that's ok) or is a regular thing.
I have emailed ex a few times about how we need to communicate more for their sakes and how I believe their behaviour may be suffering due to lack of consistency between our homes, but he never ever replies. After the last one the dc did mention him buying a couple of boardgames (first time he ever bought anything for them other than the wii) so I assume he had taken some of what I said on board, but this issue is obviously more serious than that. If I email, I won't know his response because he won't fucking communicate. DS1 has asked me not to raise it as it will make him worse . I've said no one should ever be hitting him and we need to sort it - but how?
I just don't know what to do. Ds1 says he wants to go, but not for any long stretches and has started saying he loves me more, ds2 is defending his dad and wanting to go for half of the half term and I don't know whether they should be going at all.
Wtf do I do?