They definitely both have to be spayed and neutered with at least a month passing since their surgeries before you can start bonding, and you will have to keep them completely separated until it is time for bonding. When they are taking turns out of their cage for play and exercise, they may start getting aggressive through the cage bars, so you may have to put an extra barrier around the one who is caged at the time. They can fight and bite through cage bars.
Besides the bonding article found here, https://binkybunny.com/BUNNYINFO/tabid/53/CategoryID/9/PID/940/Default.aspx, there is another good article on the HRS site, http://rabbit.org/faq-bonding-multiple-rabbits/.
I have had good luck using an x-pen for bonding. Even if it’s in a room that’s not neutral, you can make the pen neutral on its own. Place a sheet or large towels on the floor to mask any scents in carpets. You can even drape towels or sheets on the side of the pen to hide the view of a room, although I’ve never done that. My husband and I get in the pen with the bunnies, to stop any fighting (which we’ve never had) or any excessive humping. Some scuffling and humping can be normal. Start with a few minutes and increase the time each day.