Yes, at least some cats can be toliet trained. But I don't think its a good idea, because I've heard many stories that toilet trained cats suddenly start doing their business somewhere else, like in the sink, in bathtub, or beside toilet. Also if you are going to move, you have to retrain the cat, because cats don't understand that all toilets are basically the same. So I think it's more trouble than good.
Don't. ever. train them to flush! It's highly likely they see flushing as a fun activity and will flush whenever they are bored. Such a waste of water! Also don't even think about teaching them to wash their paws! First, it's highly questionable whether they can be trained to volenterly dip their paws in water. Second, you don't want them having soap on their paw. They may not rinse well and will ingest the soap while grooming.Do they flush, and wash their paws with soap afterward?