[gemy]

Give Max some alone time with you, for walks, pets, training etc. Then the same for the young male gibby. Then both on leads, take them for a walk.
Do training with each one on the walk.

Stop the humping behaviour in the same way you would any other undesirable behaviour. You can clap your hands - say NO - and when gibby desists reward the good behaviour. You can physically intercede by gently pushing gibby away from Max.

Humping is not always a sexual behaviour, it is often times, a dominant behaviour, ie the young male wants to dominate Max.

I have full males and a full female, I stop either male from butt sniffing her. A sniff or two is fine, beyond that, I intercede with either Enough, or No more - you're done.