When was the oldest male neutered? If just recently, it could take a bit for the effects to kick in. The female in the house could be setting him off, so much so that he feels he has to compete...a pissing match, if you will.
Also, when you clean up his urine, if you aren't already, do so with a cleaner that actually states it removes pheromones. Without that in a cleaner, he'll keep peeing in the same places.
A diffuser, such as Feliway, might help calm everything down. I use it with my two ladies to keep them cordial and have recommended it to clients with successful results.