Cats don’t like succulents, cacti or anything else that’s prickly. Mine never touch my jade plant or Christmas cactus, both of which are very easy to grow. I also recommend rosemary (cats don’t like the smell or the feel of the leaves), crown of thorns (Euphorbia milii) and, strangely enough, amaryllis, which my pets avoid for some reason.
However, I’m a firm believer in giving indoor cats something green to nibble on, or they go nuts. I suggest you keep a spider plant that your felines are permitted to chew. I have one that my cats snack on every winter—and it doesn’t hurt them or the plant, which always recovers the following summer. You could also provide them with a spiky dracaena, another toughie houseplant cats seem to like and isn’t harmed by nibbling. Make it clear that these are their plants. If they start chewing on something else, guide them back to the spider plant or dracaena.
Another alternative is those popular little pots of perennial rye or oat grass marketed as “cat grass,” sold at pet stores.