A 65 is probably around the minimum to house a mated pair of either of Flames or Multicolors. Both are sort of medium sized in the dwarf angels, and full grown may be a little cramped for two. There is a large element of lucky having angels from seperate species coexist long term, in ideal circumstances, in all but the largest tanks. There is a good deal of difficulty in successfully creating a pair of angels as well. There is some difficulty in just keeping a mated pair of angels long term, and a smaller tank can exacerbate some of these issues.
@ca1ore gave great conservative advice, and if you want to do it "right" to avoid problems and extra fuss, pick one of the two species and get only one. More liberal advice is that it is possible, but perhaps not ideal, to house a pair of a single species. Should you want to keep a pair I would recommend spending some time looking at what, people in the hobby, aquaculture, and researchers have to say on the process; there is a fassinating body of information on it out there, though it is all somewhat disjoint. For Flames
@ca1ore ,
@OrionN and many others here have experience selecting and forming pairs, couple quick searches will tell you about the sexual dimorphism and the debate over ideal sizing. Multicolors are a bit rarer generally, however photos and video of pairs are actually surprisingly rare, only came across a few in my brief searches. I do know one pair was on Divers Den a while ago, and you see them singly in the fish stores, enough that you wouldn't think pairs are that rare. There is not to my knowledge, or in the regarded sources, known sexual dimorphism. If I got any of that wrong please I would love to see your pair pictures and videos, and any evidence of sexual dimorphism. They are on the shortlist to try, after my last brief and unsuccessful adventure with Chaetodontidae. (Who I am now convinced are actually gonochoristic, Trust the literature!)
Sorry that turned into a wall of text quick, TL;DR:
Good advice: Ca1ore Medium advice: Maybe look into pair of one species Bad advice: Send it
An idol fantasy of mine, in a "future" fish room, a line of 60g cubes and 120g's, to solve this exact problem: too many beautiful species of Centropyge, not enough tanks.