My experience was adding a flame when the multicolored was already established. This was in a 75. The multicolor pretty much harassed the flame mercilessly. I had to remove the flame. I would maybe rearrange the rock work so no territories are there or follow Toddtrex's advice and use a acclimation box. I now add any dwarf angels at the same time.
IMO, I don't think a 75 would be too small for 2 dwarf angels at all.