Sorry, got excited...
Wow, a 55. The pic makes it look deeper front to back. Four turtle tanks are nice. I have a 125gal and a 75gal myself with 2 RES and a west african mud.
There shouldn't be a problem, they stay relatively small(4-5 inches) along with maps and a few others. If you grow them together from babies, there shouldn't be territory problems between them. If you were to mix adults or a slider and painted in with the little guys then you may see some territory aggresion. I've seen a few tanks with a nice mix of different pond turtles and believe someone on this forum has a nice setup with a mix.