Never put a doe in with a doe who has already given birth as you'll put the litter in danger. Not from the new doe necessarily, but you'll unsettle the mother if nothing else. I wouldn't even let them 'visit' if I were you as the same common sense applies. Keep them separate to give birth. They will be fine for those 5 weeks and you can introduce them to each other again when the babies are weaned. If they were going to share a cage then I'd recommend they were due to give birth within a few days of each other and were placed together at least a week before their due date, for future reference.