I'm good with that as long as it makes sense. Like for example Dumbledore & Grindelwald in this time period. What doesn't make sense is Nagini and McGonagall. I can still excuse Flamel as he's not as "popular" of a character as McGongall or Nagini for example so if we don't see Flamel in part 3 anymore, I'm okay with that.
Putting this under the tag just in case: