It's an incredibly unfortunate thing to discover that someone you love has a crazy abuser in their life that will never go away. Unlike most crazy exes, Michael cannot go no contact, ever, because they share children.
It is what it is at this point, and in just a few years, both kids will be of age and he will not need to interact with Susan any longer, just the kids and their care providers.
Obviously this isn't super comforting when she is a million weeks pregnant and rightfully wanting him to focus on the upcoming birth. The show came up at the worst time, but this is an opportunity to get the authorities involved and bring attention to Susan's abuse since the traditional channels weren't successful.
Once this evaluation is over, I think it would be fair for Michael to focus more on Amy, the new baby, and helping her through those first few months of gummy smiles, no sleep, and the arduous physical recovery after a c-section, barring any medical emergency for his other children.
I hope Michael is still working with a therapist to figure out a hierarchy of his responsibilities, and how best to help his kids without getting sucked into Susan's attention vortex, so he can focus the appropriate amount of attention on Amy, their daughter, the new baby, and his other kids. It's a high wire act and I dont envy anyone in the entire situation. No one is getting everything they need emotionally right now and it's got to be stressful to the max.