you must have a European passport (as you imply) then Easy/Ryanair/Norwegian/
1. I think it is certain it will not be a requirement to have a EU passport to hold an EASA licence, and that's not the objective anyway. Right to work in a EU base is a separate issue, but loss of right to work in the EU is extremely unlikely, as that would be reciprocated by loss of EU citizens right to work in the UK (and they have far too much to lose in that scenario).
2. For the first two of those airlines, Brits are not in the majority, and Im guessing, likewise for norwegian.