Are you keeping a record of all these things? Have your pages and pages of this stuff for the custody hearing. This sounds devastating, whether he is two or not. He is telling you something very important with all these things, he is really openly revealing his heart and what is happening at H's house. I know what everyone else here is saying but I don't agree. I think you should record everything everyday as a visitation record, including all that you do that H doesn't help with, and all these reactions of S2. If you can settle the D quickly with full custody, do that and then get into family court and get more boundaries in place with the help of an advocate. He is two now. That is easy in a way, no matter how hard and awful it is. As he gets older, the expression of that trauma comes in ways that are dangerous (self harm, drug use, shoplifting, etc, as happened with my S). I'm not trying to scare you. Just stay clear headed and record everything in a journal.
I believe I will see the bounty of the Lord in the land of the living. Wait for the Lord with courage. Be stouthearted, and wait for the Lord.