At this age, it will change nothing but the ability to procreate. It may take the edge off some behaviors, but it certainly doesn't hurt. "Losing the boys" is not a real reason to keep a dog intact. They won't care. Most of them don't even know that their butts are actually part of their bodies. Heck, my dog investigates his rear when he farts, wondering what in the world just happened!
So no, they won't miss their ballsies. They don't gather around the big screen at game time, beer in paws, scratching themselves and grunting.
They probably WILL continue to mount after desexing- this behavior can be controlled by the humans in the household. Train them, teach them, discipline them, distract them, and in general control the situation! You're in charge, you pay the bills, you dole out the food, you decide their access rights, you can step in and separate the mounting (which is likely a dominance behavior). Pooches benefit from rules, guidelines, and discipline, just like kids! You ESPECIALLY want to do this if it escalates to a fight. Best thing to do would be to neuter them both to remove excessive testosterone from the equation, then get crates for each dog. Bathe one, crate that dog, then bathe the other, then crate him as well. Take them out on their own leashes once both are finished and involve them in a controlled exercise like a disciplined walk or group training.
How is your daily routine with them otherwise? This bathtime rumble is likely a symptom of a bigger problem.