How do i stop my 5 month old puppy from harrasing my older dogs?

Every time you CATCH HIM IN THE ACT of peeing or pooping elsewhere take him to where he should pee. Whether that be on a training pad or outside, even if he is still peeing you must do this and pooping too. But only if you catch him in the act, because afterwards he won't understand. He will grow out of it and maybe even later on might still like to play fight but not as bad. Just let your older dogs teach him a lesson. He will catch on sooner or later. Best of luck!