As others have mentioned, this could potentially work provided the bunnies are all spayed and neutered. You mentioned you are getting the boy fixed, but it is also vital for the mother and daughter are also spayed. It is critical for a female rabbit’s own health that they are spayed (not just for fertility reasons), but because by the age of 5, an unspayed female rabbit has an 80% chance of uterine cancer which is fatal in most cases. For this reason alone it is so important to spay rabbits, as well as other reasons such as reducing territorial behaviours such as marking and aggression. Also, as you mentioned you’d like to bond a trio, from what I’ve researched you should definitely consider the personalities of each bunny and if they are suited to being bonded together, as not all rabbits are suitable to be in trios. I’m pretty sure there’s a thread on this on the bonding page if you’d like to read up on it.
I’d also personally recommend separating the pair if the daughter is potentially getting hurt in the process as baby rabbits are very fragile and could become injured through excessive mounting from the mother, even if she is only trying to assert dominance.