Hi Ree, I’ve never bonded a trio and am only in the middle of my first bonding of two bunnies right now. But what helped rid of the aggression and tension between the two (and so in your case maybe what you could do with the two girls) is I first had just a few sessions of having them lay side by side while i stroked them, maybe for 10-15 minutes. I’m not sure if this step would help too much in your situation since the girls have known each other for a considerable amount of time by now, but if you’ve taken a long enough break from bonding maybe it couldn’t hurt.
After doing this for a while and, whereas it was less, still experiencing aggression, we started having stress sessions. Things like having them in a tub of very low water, (only just at their paws/ankles) and letting them splash around a bit. Or you could try putting them in a bin on top of the washer/dryer, or putting them in a bin and taking them for a car ride. If they truly are very aggressive you would want to have some kind of tool for separating them during this sessions just incase a fight STILL broke out.
I hope that might help in some way. I also kinda feel like giving up in my bonding process at times, but at the littlest signs of progress I get inspired all over again!