I’m sorry to hear about your son’s situation. I myself am quadriparetic and have home health care workers who come to the house, so while it’s not 24/7 care I do understand some of the issues that can arise. I also have two housemates who come and go as well as their friends.
Different brands of locks and SmartThings
There is already an FAQ for different lock brands and how they work in a smart things installation, so many of your questions should already be answered in that thread. 
The short answer is that both Schlage and Yale are well-engineered brands. There are a few feature differences between them, and those are detailed in the FAQ. ( this is a clickable link.)
I’m not quite sure what you mean by “outside of SmartThings.” Did you mean you want a back up plan for when SmartThings is not working? Did you just mean outside the home? Or did you mean for someone who doesn’t have SmartThings at all?
My own experience, with and without SmartThings
I started out with a Yale zwave lock on the SmartThings network. I wanted a lock that had an autolock feature because with so many people coming and going I couldn’t feel confident that they would remember to lock the deadbolt each time. And at that time Yale offered the best combination of features for me.
Unfortunately last November I ran into a problem (confirmed by SmartThings support) where the lock would just start randomly receiving an unlock command from the network. I spend most of my life in one of two rooms ( One where the lock is and another right next to that) and my service dog is trained to run over to the door when it unlocks so he can open it, so it was very obvious that this had not happened in the past but it had started happening. This went on for several weeks while support was looking at it, but we were never able to figure out what was going on. It was happening about five times a week at random times. The activity showed up in the logs, but not why it was happening.
I became very concerned that it would happen while I was asleep and my dog would let himself out, so we decided to remove the lock from the SmartThings network. At first we just put it on a different zwave coordinator and the problem went away. Later we changed to a different lock model all together, but for other reasons.
My conclusions
At this point I would feel comfortable recommending either Schlage or Yale for most homes, but not on the SmartThings network. But that’s just my personal experience. I don’t think most ST customers have had the same problems I did, although it’s also true they might not be as aware of problems as I am because I am mostly housebound. And if you have the lock set to auto relock, maybe you won’t care about the fact that it might randomly unlock since it will lock itself again in a minute or so.
I will say that overall my experience with smart locks has been excellent. It has really improved how we handle people coming to the house, especially after we combined it with a Kuna Porch light. The Kuna combines a porch light, motion sensor, video, two way audio intercom, and panic button siren all under $200. It doesn’t integrate with smartThings, but being able to see who is at the door and then deciding whether or not to unlock it, plus the use of guest codes, has been very positive for us. Here is my project report on that if you are interested in reading more: