"Is everyone going to this party?"
Is 都 and 会 necessary here?
I thought that would translate as "Will everyone all go to this party", or "Can everyone all go to this party"
都 plays the important role for this sentence; if 都 is not used, then the subject identification is not specific as to whether or not it includes "everyone" or "some people". Thus, to avoid confusion, if multiple subjects are mentioned in the sentence, use 都.
You can also use 一起, which literally means "each". The sentence is then 大家一起去這個派對嗎/大家一起去这个派对吗, which means "Will everyone go to this party (together)?" 一起 and 都 are both characters that include all subjects in the sentence.
Even though 会 can literally be thought as "will" or "can", sentence with 会 is flexibly translated as "will everyone go to this party?" similar to what you mentioned. 会 is optional since the sentence without 会 won't greatly change the meaning and the context.