I think it's entirely up to you and your wife and you shouldn't feel bad that you want to throw in the towel on bonding. You guys know your bunnies better than anyone and your judgment of how far these guys can go is probably the right way to go in the end. Bonding bunnies is so stressful - for the humans and for the bunnies.
If you had more than the two buns there's a good chance that a good rub down with vinegar on surfaces the third bun had access to would be a start but you don't have that problem. Shared territory where each individual bunny may have claimed separate as their own (it's theirs when it's THEIR turn to play and the other is safely put away) is definitely tougher. Any sane person can't be expected to destroy all rabbity scents in their living room every time they wanted to do a bonding date. Vinegar is very effective at destroying the proteins in urine so it does work, but it also stinks
I don't remember reading if you did but this one woman bonded her two boys in two weeks by swapping their cages for 12 hours at a time! She made territorial dispute an advantage!
Maybe some misdirection would be a good way to distract your bunnies in shared territory. Load em up in a big laundry basket and take them for a walk up and down a hallway they've never been to, or a basement, or in the garage... It takes them out of their element so when they go back in their bonding site they're less focused on where they are and more about who they're with. Stress bonding is a method some people find very effective. The buns get stressed out a bit in a controlled environment, and they'll seek comfort in each other. Another way to maybe bribe some kisses is to smear some banana on their noses or rub a drop of vanilla extract on their heads.
It is so funny how your buns can go so many hours uneventfully. Maybe they're having bunny conversations we don't pick up on. That picture of Conan slipping his head under Xena trying to have a bite tells a small story. It looks like he wants her attention but she's too busy for him at the moment. While she does selectively groom him, there seems to be still some dispute over who's the top bunny here. Without knowing who's really the boss, it's hard to solidify a relationship.
When I was bonding my pair, Penny tried to get Kirby to groom her and she'd try to slip her head under his head, legs, stomach... she tried! Sometimes he would oblige and sometimes he would ignore her. He would get so annoyed by her attempts that finally he did end up boxing her and got her good in the face. After a couple of times of being smacked around she got scared and she stopped trying. She did not fight back. Eventually so much "nothing" happened during their dates that I decided it was time to let them go a full day together without knowing who was the alpha still. Weeks went by before Kirby started to lower his head and demand grooming. Penny would try and refuse at first but eventually she gave in. Today, Kirby demands and Kirby gets. Penny demands rarely and gets it even more rarely. :boxing