Kribs are cichilds, so being territorial is a part of what they do. It is true that females are not AS territorial, but not all can peacefully co-habitate with their own kind.
Not sure what a 'siphlodom goby' is. Closest I could find to that spelling was Sicydium. Gobies, generally, are bottom dwellers, as are kribs, so you may not have enough 'floor space' for the three fish. Lots of hidding places, plants (real or fake), rocks, driftwood, etc. will help break up the line of sight and help them to stake out their 'own' place. I don't think the otos factor into the territory problem.