Wood shavings aren't generally recommended as they can cause respiratory problems in some bunnies...many people here just use newspaper with hay on top. Other options are recycled paper pellets, megazorb, or wood pellets (the type used for cat litter). Saying that, your life will be made a lot easier if you can get the litter training sorted - are they both neutered? This often helps. If they have a litter tray, they don't really need additional 'bedding' as they will be cosy enough indoors. What sort of cages are they in?