Two pairs would be fine in a 55 but you are going to want them to go in the tanks as mated pairs. If you just put singles in they could cross-breed pair.
I don't believe you can cross-breed Blue Rams and Bolivian Rams, so I wouldn't be too worried about that.
Blue Rams typically want a higher temperature than Bolivians, so you'd be keeping the Bolivians at the high end of their preferred temperature and the Blues at something at the low end of their preferred temperature.
Honestly, I'd stick with one type of Ram. If you have Bolivians already, I would up their numbers a bit so you get a small shoal---they really appreciate their own company (except, of course, when breeding).