You're right, not ideal but what's the alternative for surplus male gorillas,apart from the unmentionable?, I am also thinking about the keepers, four adult male gorillas living together, they will have their work cut out.
I guess they are all prepared for that. I'm sure Kesho and his two young brothers will get along fine for some years to come including as they mature. But the problems may start to arise much later when they are fully mature e.g around 15-20 years as has happened at Port Lympne. Of course there could be changes by then if either of the younger two leave for breeding groups. For obvious reasons, Kesho and Boulas are likely to stay there for good. I shall be interested to see if they do get all four together including Boulas though. If not, it means he would have to be segregated 'offshow' indoors or in an offshow outdoor cage if there is one, during the daytime, right from the start. I think they may be successful with him though.