The Overexertion modlet should only occur if they've been doing something physically stressing - like exercise or woohoo. As for the uncomfortable surroundings modlet - put walls up and look for a plate or cup that wound up on a shelf or something, because those aren't default for elders. Or a pile of garbage that somehow glitched behind a counter. Those are the usual culprits when any sim has a "messy surroundings" modlet and you can't see why.
I play with elders all the time, and even when their bedroom is on the third floor, I never had a problem with stairs tiring them out. However, they also tend to have a 7+ in fitness because the house has its own gym (I've been playing in it for 9 generations now on long life) so that may be a factor.
If they have jobs and are getting the overworked modlet, let them take some vacation days. They can keep working, but they can also retire and get some money daily (about half what the base pay is for their current job level) I don't know if that applies to babysitters though, since that's a part time job. (I tend to have my elders go through their Vacation days and then retire.)
