Trying to Plan a 90Th Birthday Party and It's Bringing up Family Drama....

Ask your mother which she would prefer. It's her birthday. If she wants a big party, go for it. Explain to your sibling this is for Mom and not to ruin her day. Your doing the work. I am assuming you are also paying. You get to make the decisions. If Mom knows the family situation and doesn't want to be bothered with a big party. A quiet small celebration somewhere is great. I am assuming she is mentally with it. If not, why go through all of this if she won't understand it's her birthday party.

Like the previous post I would ask and see what she really wants. If you don't want to ask, I would lean more to the taking her out, just the 2 of you. Mainly because I think it would be more special to spend that time together, rather then a big party with lots of people & tension, but that's just my opinion (im not a huge birthday party person).
Why are they telling you off anyway, I mean what's their problem? Regardless of the reason, this is about your mom, not them. If you really want to have this party, I would tell them to behave or don't come. I have a sibling much like yours, although he doesn't tell me off to my face, only behind my back...it's so hard to deal with. Good Luck, and have fun celebrating your mom's 90th!

I say tell them both 'Shame on you for trying to ruin Mom's 90th birthday! If you want to help, great, but no more drama. If you don't, tell me now!'

I also second the idea of asking your Mom what she really wants and go from there.

Is it a surprise or can you talk to mom about what she wants?

I think it may be better to just go out to dinner the 2 of you. Have a great time!

I would go forward w/ planning the party even if I had to do so completely one my own. I would tell anyone that is involved w/ the planning that you want to include them and would love their help; however, discussions on past disputes will have to wait until after your mother's party is over and done (if it is something worth discussing). Remind them that this is for your mother/grandmother and want to focus on her and her party.

Updated

I would go forward w/ planning the party even if I had to do so completely one my own. I would tell anyone that is involved w/ the planning that you want to include them and would love their help; however, discussions on past disputes will have to wait until after your mother's party is over and done (if it is something worth discussing). Remind them that this is for your mother/grandmother and want to focus on her and her party.

I like what Anna Lee B. said.

why were the other 2 involved in the planning? were they helping financially? if you don't need the help financially and you want to surprise mom with a party, I would just do it all myself! invite everyone and have a good time. if the negative nelly's show up, just stay away from them. I know easier said than done but not a lot of people live to 90 and i think this is something you might regret if you don't go forward with it. good luck!

The thing to do is - yes - ask your mother what she wants. If she asks about the other relatives, you might be able to get away with saying that some of them can't make it (or maybe not). But doesn't your mother have friends where she lives? Wouldn't they like to come? A party with loving friends would be a whole lot better than a party with bitter relatives.