So electric blue rams, golden rams, and german blue rams are all selectively bred color variations of the same species, Mikrogeophagus ramirezi, which means that they should be able to pair together. Pairing, of course, is about creating a "breeding" pair and not simply a male and a female in a tank. So, theoretically, you could choose two color morphs and then hope that they do pair off, which they might - someone else might have experience with that -, but when breeding you would be remixing the two color strains, which may lead to not as attractive fry.
And to answer your last question, it is generally best to stick to one male-female pair. The third fish becomes a third wheel. As a male, it will try to establish its own territory and woo the female from the dominant male, leading to conflict and possibly death. As a female, it will try to woo the male, and will be harassed both by the male and the dominant female. So, again, best to keep just one pair and probably of similar coloring.
/www.tfhmagazine.com/details/articles/electric-blue-ram-full-article.htm
