Cat Question Serious issue need help!?

We have 5 cats, and have never encountered this problem before but for the last week our 4 year old neutered male has been doing what i call a " positon", tank gets on top of our about 8 month old cat blue, which is not neutered he gets on top of him, he doesent actually hump, he only gets on top and makes the weiredest meow ive ever heard he also bites onnthe scruff of blues neck holding him down, we have another kitten skittles which is also around the same age as blue and shes a female, i havent noticed any signs of heat, could she be coming into heat and our older cat is confused with the wrong cat?, but that brings up the problem of him already being neutered, so he shouldnt have the urge to do what he is doing, both our kittens are from a different litter and have an appt to be spayed and neutered next month so is this a heat or dominance issue and should we move up the appt? they are still small so idk if the vet would do it but it wouldnt hurt to ask, any ideas on why my cat is doing this? besides the fact he must be gay?