Hi oj, not been on one of your threads in ages, but I am keeping up with your news and thinking of you, Steve and the children.
I think that the staff at the hospice have got your MIL's number, they're just being very cautious over what they pass back to you. I expect they agree with you, and have a similar opinion about your MIL. They have Steve's welfare to consider first and foremost, and I think it will be obv to them that going home with MIL would be a disaster.
I don't know how, but I think you have to make Steve in some way wary of going to his mum's. It's not kind, or fair, to do that, but you're in a horrid position and needs must an' all that.
Thinking of you.