Hey thanks for the advice! I also considered putting collars on them for this kind of bowl that only gives access to the cat with the right collar on which sounds neat but I'm not sure if it's so effective at keeping him quiet (wife works at home).
Regarding the teeth, I'm not against their removal so to speak, but the anaesthesia at his age is a risk many vets aren't willing to take especially at his weight.
I don't want bad teeth to cause kidney diseases but at the same time I don't want him to die trying to reduce the risk of that. It's tricky...
Sadly, yes. Weight loss should be gradual to avoid complications with his liver because cats don't process fat very well but if you can get his weight down, it's worth a try. Don't reduce his food intake by more than 10% every couple of weeks. The Hills metabolic diet kibble actually worked well on my little butterball when I used it