I have 3 feral cats. 2 males and a female. I've never trimmed their nails and wouldn't consider declawing them. Mine all learned the rules, know what they can and can't scratch. I also have a jack russel that knows and will enforce the rules. When the cats step out of line or start fighting, which happens every day, then the jack russel will straighten them out. If I call the cat's name, in a positive tone, they will come to me... If I call out their name in a negative tone.... the dog will bring that cat to me.
The oldest male cat hissed and clawed me once... When he did... I picked him by the scruff, lifted him to my eye level and asked what he wanted. He never did it again. If their claws start to dig into me when petting, or sitting with me, or similar... I flick their paw gently.
My cats don't wear their claws down enough to go without trimming.
You should check yours, it can be painful for them.
One of mine also had tooth decay problems. His plate fractured and was giving him a canker on the side, where what was left of the teeth rubbed. He was ornery while that was happening, and it wasn't until a while after we had his shattered teeth pulled, that he calmed down.