I am 18 and I have known and been round my nan all my life she was there when I was born and through the problems I have had.she was always a little manipulative and controlling and she never really new when to stop. I have 3 brothers and sisters (4,9 and 10) she has always looked after them after school till my mum can pick them up.
Over the past year mabe she has been making comments that are really upsetting my mum. Before easter we were all going to have a family picture paid for by my nan but my mum said she didn't want to be in it (appearance issues) and my nan deiced to cancel the whole thing because she didn't get it her own way.
But the worst was over christmas, mum and nan and an argument over who was coming and where we were going to have it, so it ended up with them throwing wine over each other and the kids going home in tears because of all the shouting. So when christmas came nan and grandad went to my uncles and my brothers and sister didn't get any christmas gifts from them because of my nan holding a grudge.
The whole thing is splitting my family up and I don't no what to say because I don't want to offend my nan and her to stop talking to me (happened before) but this can't go on.
I don't no what to do I need help.

I love her to bits I really do but I don't no what to do

In view of her Parkinson's disease (https://www.askmehelpdesk.com/medical-conditions-diseases/what-will-happen-her-312004.html) and the behavior of your siblings, which you have questioned (https://www.askmehelpdesk.com/children/why-dose-he-scream-318076.html) which causes your parents to argue and a neighbor to call the Police, maybe she just can't handle the stress right now.

Its my nan on my mums side not my dads. My nan on my mums side has no medical conditions as far as I know

That is too bad and it probably won't stop.