If your cats are nibbling on plants they are lacking something in their diet. I buy Indoor Cat by Purina which contains greens and don't have a problem with my cats but I also grow catnip just for them. So far so good.

There is NO need to feed them.

Your cats MAY damage them if you don't keep them away from the plants somehow. The Sarracenia is an OUTDOOR plant, the others you mention for the most part are indoor plants unless you chose a temperate Sundew and Butterwort instead of a tropical. Get tropicals.

Yes, cats might attack your plants, but I don't think they like carnivores any more than they crave other greenery. Ugh, one time I was trying to grow vfts in a shallow round container. For some reason, I brought them inside one night and left them on a shelf. One of the house cats is notorious for eating plants. Next morning, the dish was knocked over and the cat was puking up vfts and the flies inside them.

No need to feed butterworts or sundews. Fungus gnats will find them, and then the plants will trap the gnats. Built-in food supply.

Agreed with the fungus gnats keeping the butterworts and sundews fed..mine are absolutely covered! As far as the cat, mine has attacked one of my d. adelae's TWICE (and he gets the indoor cat formula food too), and the 2nd time I thought I had put it somewhere out of his reach. However, I re-purposed a shallow rectangular plastic pan by filling it with peat and planting catnip, wheatgrass and birdseed. I covered it with a clear cover until everything sprouted(it was a container from when you buy roasted chicken at the grocery store, works perfectly) and now naughty Eddie has his own indoor "lawn" to keep him busy. No problems since!