I'm seeing this post later than I'd like to, but your kitty sounds fairly healthy given their age.

My little (large) - she's ~5.2KG Mia has similar things - she's overweight for her size, has had a cyst drained a few times on her belly, but it otherwise healthy.

With regards to the arthritic stuff in the cat, there's an injection that can be given to them (3 rounds a few weeks apart, then 6 monthly thereafter) which helps with the joints. Its something that is in human trials now, and it works, she's like a new cat everytime she gets a shot of that juice (whatever it is).

She's coming up 12-14 years (we're not entirely sure, as we adopted her when she was assumed to be 6 - and have had her for about 8 years now) - and now that it is getting cold at night, she's become the annual winter snuggle muffin, and its just adorable.

Have you tried adding some water the wet food in addition to the jelly that comes in the can / pouch / however you fed them? This increases their fluid intake which can help with the erosion of any kidney stones / issues etc.

Edit:

Also all the best for your human mouth, hope it isn't painful