Sorry, longish post, but I've never been in this situation before and want to do what's best for the children.
My DS (10) has become best friends with "A" whose parents are separating. I don't know if A is aware of the situation as they're still living in the same house and co-parenting A and his sister.
We've only known the family about six months and until about Christmas, everything seemed amicable - but now it's completely changed. Last time I collected DS from a play date, there was a horrible atmosphere between the parents and the Mum asked me to stay for a cuppa...I think it was to defuse the tension, but it didn't work, Dad was civil to me but wasn't speaking to the Mum at all.
Then, I received a frantic text from her asking if "A" had said anything to my DS about where he was going that weekend, as the Dad had taken the children away for the weekend without telling her where they were going. I talked to my DH about it and we decided to text the Dad asking if "A" could come over for a play date... thus we found out that they were returning on Sunday morning and "A" came to play that afternoon. I didn't want to get involved, but no one should be treated like that, the poor Mum was really worried.
Then the Mum invited DS to play this past weekend...but 24 hours later, "A" told DS that his Dad said he isn't available anymore. OK, fine...but the Mum texted me the morning of the play date...she didn't know it was cancelled.
I DON'T want DS or I to be stuck in the middle of their feud, but I also don't want to abandon "A" who probably has no idea what's going on and will need his friends in the coming months. 
Should I just keep inviting "A" to our house and avoid play dates at his?