Hiya, welcome to the Forum Cycas
I am sorry to hear of your difficulties with your two rabbits, Elise and Amber.
I think that they have sorted out the hierarchy of which is the Boss rabbit inside the rabbit house as they spend a good deal of their time there.
However they (I assume) have less frequent access to the garden, so each time they are fighting over territory.
There are several options, firstly, accept things as they are and just allow one rabbit out at a time, at least this is better than nothing.
Section two areas off within the garden, perhaps with wire mesh panels (Look at the Rabbit Rehome web site for these) so the rabbits can run along side each other in the garden but not actually together just yet.
Swop them into a different run each day so neither sees the wire run as theirs..you are teaching that it is shared territory.
This is difficult on a garden sized scale though
Do they run straight out of the rabbit house into the garden?? or do you lift them out?
Do they fight immediately once in the garden, or do they amble around for a bit before launching an attack??
How often have you allowed them out into the garden? Daily? Once a week?
Sorry for all the questions, but just trying to get a clear picture so I can think of some further ideas.
Ps. It is fairly typical with Does to be extra territorial, have they been spayed??
PPs. Do they have things to hide under and get away from each other in the garden, or is the area all open.
I am wondering that they are feeling vulnerable in the garden for some reason, and perhaps the flight response is triggering a FIGHT one..bunnies can become aggressive through fear..perhaps they need a lot more reassurance that the garden is safe...and providing lots of cover is a good option to help.