I'm assuming these are wild rabbits? If they're the kind you normally see in the wild, the mom could still be around and looking for them. Rabbits usually only nurse at night, then stay away from the nest so they won't lure predators to it. It's common to think the mother either abandoned the nest or was killed if you don't see her around. It's always best to leave a nest right where it is and assume the mother rabbit will be back.
If they are still nursing, keeping them alive without mom is tricky and labor intensive. They need to be fed kitten formula, since their nutritional needs are similar to kittens. However, they have to be fed precise amounts and more often than the mom bunny would nurse since they're not getting the exact milk they would get from her.
I think you have a couple of choices. Put them back exactly where you found them and hope the mom comes back. Or, take them to the Humane Society. They might be euthanized right away. Or, a rescue organization might take them from there. Sadly, they likely will not survive if you keep them. And they will not make good pets. They're much different than domesticated rabbits.
It was a good thread though because you opened up a door of information. I have learned so many things over the years here. Ruthie
12 weeks is way past them being able to live on their own, so it sounds like they will be fine 
