how do i get my cat to stop fighting his brother?

i have two cats that are brothers (from the same litter and have been bonded since birth) an orange cat and a tuxedo who are both boys and 3 years old. they’ve always fought occasionally as cats do but i moved into a new place like 8 months ago and the fighting has gotten so much more frequent.

it’s always the orange one who starts it and he usually always starts by mounting his brother and biting him between his shoulder blades. i get it’s him asserting dominance, but he’s started doing it several times a day, and specifically if i am in another room. for example, the orange one ALWAYS does it if im using the bathroom and he knows i cant easily stop him. i’ve started having to take one into the bathroom with me.

how do i get him to stop doing this? i feel so bad for my other cat and he always starts yelping so loud when it happens :((((( i can’t keep them apart because they’re bonded and start crying for one another.

idk if this adds some context or is even related but the orange one also humps the tuxedo sometimes (specifically when he’s sleeping) which is so gross but he’s been doing it since they were babies.

i’m not a minor, in the us, vet is accessible but haven’t contacted them

TLDR: how do i get my cat to stop mounting and biting his brother several times a day?