Caring for feral cats that come and go

There use to be a few feral cats that would come around that I would always feed and try to be friends with.  A few years ago, one came around, looked middle aged, kinda skinny, pretty coat, gorgeous blue eyes. Definitely looked like he was someone's house cat that got put out to the streets. He never really wandered too far away from my place so I gave him a name & called him mine.  About 6 months later another one showed up, this one was young and looked like he had been fighting for his life since birth. I could feel every little bone in his poor body. Once I got that little guy back to health,  he stuck around pretty faithfully.  The other one was still around too, just not as much as the younger one. They got along with each other pretty good for both of them being male. I take the best care of them that l can, but they do both still have a little wild in them it seems that makes taking care of them difficult sometimes. They don't like to be picked up or pretty much anything that is too much inside their personal bubble they get nervous and run. They live outside,  I've tried to get them inside but they don't seem to trust indoors too much. I have gotten them to come inside for short periods of time but they are always anxious to get back out. I worry about the older one being out because he roams more and comes back looking rough but I never know where he goes.  I just wish I knew if there was an easier way to know what's goin on with them, or monitor them somehow maybe.  Are there some subtle things I can do for their health that they won't even notice,  I just don't want them to get scared but I don't want them sick or anything either.  I think the older one may have some kind of dental issues.  I'm not even sure how old they are. I've somehow never once seen the younger one even go poop. He's very secretive with that. I just want them happy and healthy as I can make them.  Any kind of help is greatly appreciated. Thanks for reading my long story.