GBR's, Bolivians, Kribs, and Apistos can pretty much be kept together in just about any configuration, as long as you have room for them to create their territories. I know people who breed kribs, and have GBR's in the same tank, and no real problems. Just don't do it in a small tank. I believe his tank is a 75G with the GBR's and kribs, and 1 pair of apistos.
I personally keep 3 Bolivian Rams and 7 pairs of GBR's in my 75G with several tetras, plecos, cories, and more.