It is tricky being the weekend. If it weren't Id try and get SS to call exP to clarify how he should be dealing with DS.
HE is his son too, and although he may not be the best influence, he does care for him and will want the best for him.
Regarding your brother, what a bloody idiot. I agree that it isn't worth wasting your time on that at the moment. You have enough heartache, falling out with your brother for being an idiot when you need as much support as possible won't help things.
I hope that you have told the girls how proud you are of them and how brave they were.
I also think that DD2's illness may be psychological. It is quite common for emotional problems to manifest themselves in physical illness. DD2 gets time alone with Mummy when she is poorly, something that she probably needs.
What did SS say about how they want to deal with the girls? Are they being offered therapy? When will this start?
Did you get a change to talk to SS about possibly getting a house transfer?
What is the timescale with the police and SS now? You think there might be a police interview with DS1 over the weekend? What else? Have they arranged to see the girls again?
Have both schools been informed?
How are the DDs this evening? In bed I assume, but how were they after school, apart from DD2 being sick? What have you told them about the future? Have you got any nice plans at all over the weekend? It might be a good idea to think of something lovely for the three of you to do while DSs are away. Maybe baking, or a firework display?
I hope you are OK. I wish you all the luck and courage in the world. :)