Do zebra finches need to be in pairs?

[Celeris]

zeebeez

I'm not certain that there's a definite answer to this particular situation. If I were in your shoes, with birds that are adapted to each other, I would wait and see if any trouble arises. If I saw anything beyond the typical bird beak sparring/occasional squabble, I would start separating any trouble makers/bullied birds (depending on the ratio.) But I would not remove any birds until problems arose.

While Sojourner has a point about inbreeding, if you're not letting them sit on the eggs, I really wouldn't worry about removing birds just because they're related.

That is what I would do: leave things be and observe, then take action if needed. You have a better idea of what's going on in your little "colony" than any of us do.