Hi Michelle,
Kittens "suckling" on a male litter mates genitalia is not entirely uncommon among cats that have not had a sufficient time with the queen. I had bottle babies last year, and one of the males was suckled on so severely that his little organs built up scar tissue, the prepuce swelled shut, he wasn't able to urinate properly and he had to have a major surgery at about 4 or 5 weeks of age. That's just an FYI, because your cats are older and I'm assuming the one that is pounced on and licked, etc. is urinating ok.
It does seem like dominance behavior, hopefully the neuter will calm the little fella down, but it can take up to a month for the testosterone to leave his system.
Esther