hi
are they neutered? I'm presuming not.
how old are they?
rabbits should be neutered/spayed at anywhere from 3-6 months, depending on their weight and when the males testicles drop. a rabbit savvy vet can preform this with little to no complications, of course there is always a risk with anaesthesia, as with any animal, and in rabbits it is higher. but with a rabbit vet that knows what they're doing, it should be smooth sailing, and if its not they will know how to act upon the situation.
having a vet that isn't rabbit savvy can mean the difference between life and death due to them possibly not knowing what to do, or even giving you ill advise.
rabbits need to be separated from at the very latest (in my opinion) at 10 weeks old. boys have been known to breed at 12 weeks of age. its why at 8 weeks breeders separate males and females to stop any chance of breeding happening, among siblings or to mom.
usually they can't impregnate a female before their testicles drop but this is not an exact science as they have been known to impregnate females before their balls drop.
rabbits should be neutered/spayed for a number of reasons, the most being for does(girls) that uterine cancer is rife. a lot of does that haven't been spayed often seem to get uterine cancer or infections, and it shortens their life span. for boys, its mostly behavioural reasons, same for the does too. a neutered/spayed rabbit is a healthy and happier rabbit, not controlled via their hormones and the stress of not passing on their genetics.
many unfixed rabbits are territorial, grumpy and aggressive, towards you and towards their partner. in many cases with unfixed rabbits where one or both aren't fixed, the bond breaks due to hormones and aggression, and fights occur.
here is a guide to sexing rabbits:
http://www.pet-informed-veterinary-advice-online.com/sexing-rabbits.html
here is some information on spaying and neutering:
https://rabbit.org/faq-spaying-and-neutering/
https://www.vets4pets.com/pet-health-advice/rabbit-advice/neutering-your-rabbit/
https://www.saveafluff.co.uk/rabbit-info/neutering-spaying-rabbits
if you need help finding a rabbit savvy vet, check here:
https://rabbitwelfare.co.uk/rabbit-care-advice/rabbit-friendly-vets/rabbit-friendly-vet-list/
OR, you can ask in the forum with your location and somebody may be able to offer a vet that is good.
I am not sure if you are aware, but rabbits also need vaccinations, myxi, RHD1 & RHD2. there are two different vaccines, filivac covers RHD1 & RHD2, nobivac covers myxi & RHD1. they do need both and without the vaccination, mortality rates are high.