Honestly, if you’ve had them this long and attempted bonding so many times, I think it’s unlikely. Female pairs are meant to be hardest to bond, so I assume a female trio is even harder!
That said, if you want to give it one last go, I suggest you keep them totally separate for 2-3 months so they forget each other and their fear of each other. Then move them into one room (with double bars between them all so they can never reach each other or fight, and rotate their cages daily so they all get used to smelling each other and lose a sense of territory. Do this for at least a month, and do it even longer if you still see aggressive signs between them.
After that, you can try introducing them in a totally neutral territory for one minute. They don’t even have to interact at first, and you can keep your hands between them if you’re worried about aggression. The next day, do 2 one minute sessions, then 2 two minute sessions etc. Gradually increase the time they’re spending together and gradually intervene less when you’re confident they won’t fight.
I did this with my trio, (2 boys and a girl) and they are all very happy now. I wish you the best of luck!