Do you have enough accomodation for them all? The boys may need separating and of course the sexes need separating. Plus then if the girls are pregnant they need to be separated, and then when the litters grow up the boys need to be separated out.... Are you sure you have the space, it can get out of hand quickly. Could you bring any inside (but theyd have to stay inside till April).
If space is an issue it may be worth just taking the girls for now, to stop that person having any more accidental litters.
£300 isnt going to go far with neutering, you are right to get help with it, an average neuter would be £50-90, then you need metacam on top of that...
I'd also find a supplier asap for baled hay if you dont have any already, as you are going to go through a lot with so many hutches.
You may be able to get the baby girls an emergency spay if they are not too far gone, but you would have to act fast and get a vet to check them to see how far along they are.