I’ve been involved in rabbit rescue for years, and they absolutely need to be kept in pairs or groups. Out of hundreds of adopted rabbits, we’ve come across a tiny handful that are genuinely happy as singles, and this is only decided after they’ve had multiple failed bonds.
I’d bet my life the posters blithely saying ‘some rabbits are happy on their own’ is due to a complete lack of understanding of the bonding process, I see this all the time on rabbit groups I’m on.
OP, as they’re from the same litter the sex doesn’t matter, they are already bonded, but it’s really important that you get them neutered as early as possible as when their hormones come in they’ll unsettle the bond.
For such cute creatures, rabbits are very territorial and will chase, nip, mount etc to establish their position as the dominant bun in the pecking order. It is possible to re-bond if this happens, but much much simpler to just get them neutered on time.
The RWAF website another poster linked to above is a fab resource and I’d highly recommend using that as your first port of call for any questions you have.
Please don’t go to Pets at Home or similar and buy a hutch and run - most places sell products that don’t meet the minimum size requirements, to meet their welfare needs they should always have access to at least 10 x 6 ft of space (but the more the better!) Typically this would be a 6 x 2 x 2 ft hutch connected to a run at least 8 x 6 x 3 ft.