Contact Legal Aid first thing.
I personally would never be splitting my kids. It's not like dividing assets ffs! They're kids. TBH, I think kids find it a lot easier when their siblings are with them... having my parents split wasn't too bad in that I no longer lived with Dad, but if Dad had taken my brother and I was with Mum, it'd have been really difficult. I liked that I had him around who was going through the same thing.