((((((((((depchild))))))))))
I'm sorry that you are stuck in the middle of this sticky situation.
I know you are worried about your mum(and I will address that in a sec) but I kind of feel sorry for your dad. Why are so many people against him??? From what you've said it sound like he's not getting all that much support.
As for your mum, do you think that maybe someone has planted the idea that your father is cheating?? It sounds like people she is close to don't have a lot of time for your father. Do you know if there is a reason for this? Has something happened in the past??
Have you maybe thought of sitting your parents down and telling them how much their arguing is effecting you? Maybe they don't realise how much pressure they've put on you, and I'm sure the last thing either of them want is to hurt you.
Good luck and keep posting. Let us know how things are going.
Feel free to PM me if you want to talk.