Nala and Simba both have their own crates in the bedroom that they sleep in. Now that they're older, I can leave the doors open and let them sleep where they want. Nala usually walks into her crate for the night while Simba usually flops down on the floor somewhere.
The last couple of nights though, they've been sharing the same crate at night. Simba just walks in there, curls up in the back and uses Nala for a pillow. She doesn't seem to mind the company and hasn't kicked him out yet or anything. It's kind of cute to see them both in there.