FIRST off..........
Second, it is really your choice if you want them together or not.
Short story: We started with our first two girls together in a 55gal. Everything was great per say but Huggie Bear never missed a meal and Lynn would only eat every other week. Not big issues right? Well after separating the two, they BOTH started packing on twice as much weight than they did when they were together. Why, I dont know but they also seem to shed way faster too. Only thing I can think is less stress? Who knows