If you don’t have room to house 3 rabbits at once, you should decline from taking all 3 of them in. Even if you were to bond two, that can take several weeks (under perfect circumstances with all parties spay/neutered), during which time they would have to be housed separately anyways.
I would also caution against creating rabbit pairs when they will be going up for adoption. Not everyone wants a pair and they can be much, much harder to adopt out. Once fully bonded, they should not be separated as both can go into a serious depression upon losing their mate.
It’s very kind of you to work with a local rescue and help foster buns, BUT it’s incredibly important that you understand YOUR limitations as far as time, space, and money. You can help, but don’t take on more than you can reasonably handle. There will always be another rabbit that needs fostering, but you have to be firm on how many you can take and stick to that number.