I don’t know of any age or size charts, since size can vary so much between breeds. You will find a lot of good rabbit care information on this site. Click on BUNNY INFO at the top of the page to read about feeding, housing, bonding, litter box training, bunny proofing, etc.
Hopefully the vet can approximate their ages and can make sure of their genders. Rabbits can reproduce at a very young age, so they will need to be separated when they approach 3 months old. Even if they are the same gender, once they reach that age or a little older, their hormones will kick in, and that can lead to aggression and fighting and injuries. At that point, you would need to separate them and have both spayed and or neutered. Then after a few weeks of recuperation, you could start the bonding process. Since they are babies now and evidently pretty small, the 2 x 3 cage is probably okay, but they will need a bigger cage or x-pen to be in when you are not home and they don’t have free roam.
If you have any specific questions, feel free to ask them. Welcome to Binky Bunny!