My parents are getting divorced....?

Right, basically my parents have always had problems which escalated when my mother had an affair 2 years ago (which recommenced this year) and now obviously the divorce is pending. I haven't gotten on with her since the first time (I know this sounds like a ranting teenager but all she does is deliberately try to argue, by this I mean, she tries to over yze everything I say to make it an offense to her then moans at me about it or constantly makes ping bitchy comments in general conversation even when my friends are present). All this has done has made me more reserved and unfeeling towards her even though I have pointed this out she blames my father for the outcome for not being emotional with her. Little is done to rectify it, both parents moan to me about the other as both want me to visit them more than the other. I have a baby brother who is honestly my world and it seems his whole world is going to change (he had learning difficulties and isn't very adaptable to change especially at this level) and my mother has already mentioned she will try to take more of him whilst subtly threatening me to visit whilst my father just cries over the situation and I honestly don't know what to do? I want to spend as much time with my brother but my mother does taint his persuadable mind against the rest of us (I hear her do this) Please help as I'm a confused 18 year old who perhaps is too close to the situation to view it clearly.