The article «os» gives it away: «Nós somos os próximos.» literally means "We are the next." In English, you do not say this, so you have to add "ones" at the end. Without the article, «Nós somos próximos.» would mean "We are close" in relationship. For destination, I think the adjective «pertos» would be more appropriate.
Actually, what we native English-speakers would always call out if someone jumped in front of us in a queue is "We are next" or, more likely, "We're next!". You will absolutely never hear anyone call out "We are the next ones" or even "We are the next ones to be served". I was astonished when Duo came up with "We are the next ones".
That sounds awkward to say in English. I would translate that Portuguese sentence as "We are the next ones to receive a ticket." «próximo» = "next," and «seguinte» = "following" (from the verb «seguir» = "to follow"). However, if you feel that the English sentence does not sound strange, feel free to report it.