I absolutely would not recommend keeping a 5 week old baby by itself. It's much better for them to have company at that age.
Most rabbit breeders will not sell kits under 8 weeks old, and to be honest, it's illegal to buy or sell them at 5 weeks in many states. (Both PA and NY for example.)
As to getting along, the problem is that no one can really predict what a rabbit is going to do at or after puberty. They might be OK, they may mount each other incessantly(yes, females sometimes do mount females), they may injure or even castrate each other.
Spaying or neutering can help reduce those behaviors...but I've seen a few posts written by people who didn't understand why their spayed/neutered rabbits still fight.
I'm not saying that two rabbits cannot be kept together, just that there will some risk involved, and you should have a backup plan for if they can no longer share their space.