'Are you vegetarians?' would be «Ви вегетаріа́нці?».
(There's also a female form, «Ви вегетаріа́нка?». However, it's optional: you can use the male form веретаріа́нець when addressing women too.)
In American English we commonly say "are you vegetarian?". This asks what you are, not what group you belong to. It's conceivable there is nuanced meaning to the Ukrainian sentence which would make this not the correct translation, however I have reported it as an alternate translation.