Rabbits really do best in separate cages. Especially if you have both bucks and does. Otherwise you will quickly be over run with rabbits. Bucks will fight with each other, most does will fight with each other. They really are solitary animals. If (however) you mean to put straw under the cages, that would be fine I guess. I can't really comment on rabbits on straw as ours get hay every day, but have never given them straw. I don't suppose it would hurt them, I know ours love the oats they get as a treat now and then, and straw is made from oats. Hopefully someone with more knowledge on the straw part will come along soon.
we give ours straw in the winter time for extra bedding and they love to eat it. But we bale our own straw so we have plenty! Our straw is Wheat Straw and has lespidiza mixed in. They love it. I don't give them a lot because they will start to pee and poo on it-instead of eat it. I mainly only give it to does that I know are going to start nesting soon. We feed some fescue hay too, when I feel they need it-usually in the winter. My rabbits get to munch on grass almost every day. And I agree seperate cages are better for most. Especially if you have does and bucks. If you leave the all together they will breed and rabbits like other animals don't care if they are related. You really don't want a brother and sister mating. You can do daughter father but shouldn't ever do mother son.
I would not unless it is for warmth in the winter for for a female to use while building a nest. The problem with straw as bedding is it tends to get saturated with urine, then the rabbits stand and lie down in the urine straw. The combination of the urine and the dampness can cause irratation and sores on feet and genital area. If you are planning on changing often to make sure it is 100% dry then go for it. I prefer to have mine in wire bottom cages with wooden resting boards. Make sure the wire is thick and galvanized so as to provide enough support for the rabbit.
