Aggressive sibling jealousy

[QueenGrapple]

I am in a tough situation with a neglectful coparent and a joint custody order. We are currently working through filing medical neglect, which leads me to inconsistency in households. When the kids come home from their dads my 5yo has extremely aggressive jealousy towards my 7yo. I have caught her choking her sister saying “stop trying to be cuter than me” as well as my 7yo coming home with deep scratches on her body saying her sister got mad at her.

I have tried many tactics, but it seems to be getting worse and she is more easily angered. I cannot control what happens over there and the communication is nonexistent, I’m just at a loss with how to help her convey her emotions without harm.

Can you each have the DC mostly on their own and they are only with the same parent a couple of days a week?

Unfortunately we are at one week on and one week off and the stay together. He doesn’t allow contact with them when he has them but it’s like teaching her over and over again when she gets back.

Have them alternate weeks?

WTH goes on at his house??
Keep trying to nurture their relationship. Have strict rules around how they're allowed to talk to each other, get them out and about and exercised and keep reinforcing the message that they're sisters and that relationship is for life.
Get them involved in doing things together, whether it's watching a film, tidying up, setting the table or playing.
Good luck with this. Sounds awful.