Cats and Rabbits - Advice?

As most of you know Bun-Bun lives with me now. Feldspar chases Bun-Bun around sometimes, though Bun-Bun has hissed at her now, and will bite her before she knows it. Jasper ignores Bun-Bun.

Feldspar climbs in Bun-Bun's cage, and wants to use his litter box, which has Yesterday's News in it. The cats' litter box has clumping clay in it.

Queries: Can the cat and the rabbit share a litter box? Should i buy Yesterday's News for the cats?