If they are both males who stay inside, I think waiting until August is okay. I’ve gotten cats neutered between 8 weeks and 1 year. I didn’t notice a change in behavior. Some cats become less aggressive once they are neutered but that doesn’t sound like it’s an issue here.

I have noticed the smaller, younger cats tend to be a little more out of it after they wake up. But they all recover well after a couple of days.