As MyBunnyBoy states, mounting is mostly adominance thing with rabbits and has nothing to do with mating.However, with little ones watching, I understand your situation.
It is possible to have a male/male bonded pair, but it takes a lot ofwork to get them to that point. It is very well possible that it couldtake some work for a male/female pair as well, which I have a lot ofexperience with. Currently, I have three rabbits, two bucks and a doe,all bonded and sharing one (very large) cage.
What you want to do when introducing, is not just put them in the samecage, or even out in the same area right away. It doesn't sound to methat your current male was aggressive persay, just establishing who wasgoing to be "top bun" of the group. Next time, try letting the new bunout in the shared area to mingle his/her scent with your first rabbit.Place their cages next to each other so they can see/smell one another.I highly recommend having two cages to start with. Think of it thisway, how would you feel if your rabbit brought some human home andthrew them into the mix? lol
When you do let them out in the same shared space, supervise closely.It helps to have a water bottle (the kind you use to mist plants) onhand in case they do fight. In mostcases, expect somefighting and fur to fly, although there are instances of love at firstsight. I was lucky when I introduced Abby (then 8 weeks old) toChompers (he was 3 and neutered). It was love at first sight with them,but when I brought my third rabbit (male), she was very aggressivetowards him. Chompers thankfully is a very mellow rabbit.
If they do end up fighting a lot, then you will need to take steps tobond them, which can be time consuming and you will need a lot ofpatience. It took me two full weeks to get my dominant rabbit Abby toaccept Valuran into the herd, but it was well worth it. Feel free to PMme with any questions you may have about bonding and introducingrabbits.