It's not frowned upon, but it isn't the most easy way to raise rabbits, needs more space than two minimum cages, and one has to like to do it that way. There is a learning curve for sure, but for me totally worth it. A lot of the joy raising rabbit brings me comes from their interactions.
I always keep my breeding does in pairs, there never ever was a problem with the second doe and the kits, they become pretty good stepmums and take some stress off the mother. They are social animals after all.
It can be somewhat tricky if both does have a litter, making sure they use the right nestbox and that the kits don't go to and fro if they are not the same age until the smaller ones are about 3 weeks, my setup is two hutches per pair, connected with a tunnel which I can close off easily to give a doe privacy or to make her use the right nestbox, never seperate for more than 2 days, uand they get garden time together. I use 6-8" boards to block older kits from trampling the other nest and raiding the milk buffet.
I keep the box in as long as they use it, 2-3 months. Those are closed solid wood boxes, rather big with one entrance.