BUNNY QUESTIONS, please help thanks.?

Ok, well I've had my bunny since like December, and my sister has also had her bunny since then, (we got them at the same pet store), and we never knew their gender. It is actually still unknown, and I think my bunny may be female, but it's a guess. They've been mating, though i don't know if they could both be girls/ both be boys or so. My bunny, Mittens, looks like he/she's building a nest. If they were opposite gender, I think one of them is probably pregnant. I went upstairs and saw that my bunny was being all crazy in her cage (they are in the same medium-sized cage!, we let them out in the morning in a really huge cage outdoors till it gets cold/dark) and my bunny is pulling cardboard from a box and putting it in a mini box/house in the cage. She keeps the cardboard in her mouth and rubs it all over the cage, on the door, wire cage walls, box, everything. I don't know why. We don't know the gender or if one of them may be pregnant!!! I'm 13. We are going to start separating them, other then leaving them out in the really big cage outdoors.