They are all long-haired Maine Coon mixes, and they all groom each other - it is Cat-Stock over here - free love and all. In order to "minimize" the issues, I get their undercarriages (bottom of the chest to up the butt area) shaved every few months, and Onyx gets a bath (he's got itchy skin), plus I have them furminated, and I curry-comb them once or twice a week. AND they get hairball treats once a week. So I think it's just that Loki binge-eats and then pukes. And then goes back for more. I have NO idea how the other two stay fat - they both appear to be nibblers who are not seen eating that often, nor for very long when they do eat. Though I probably give them too many treats when we have "treatie time" twice a day.
Once this Giants-Nats game is over I'm going to PetSmart to buy harnesses and leashes for them, to get them used to wearing them before their playpen arrives; we will let them get used to the playpen INSIDE, and then we will start getting them used to going OUTSIDE in the playpen. I want to take them with us in the RV.