If the plants have had time to grow in the same pot for a while the roots may have grown intertwined. Separating them could damage the roots if this is the case. It probably would not kill the plants but it could allow a fungus or disease to enter through the broken roots. I think cut roots need to be dried out for a few days before replanting???

For sunlight and growing conditions.... it might be necessary to split them up, some cactii like conditions that are hostile to others. Once you have ID you can check online for growing conditions at a site like

http://www.desert-tropicals.com/Plants/Cactaceae.html

Thank you for your response! I will certainly be mindful of the interwined roots issue which I hadn't really thought of before.

As to their individual care, I'm not certain of the conditions each would prefer as I still have not gotten any closer to identifying them.

I do believe the shorter cactus in the back (between the two thinner, taller ones) is a Mammilaria Prolifera Texana but that's all I know.