Look at reelyActive which was created exactly for this use case. FIND is also a good option which uses WiFi triangulation.
I would not deploy OH instances around the house to solve this problem.
I did go forward with this and have been running for over a year. But pay attention to the use case. I’m running this RPi over 100 miles away to keep an eye on my dad. Running a separate OH instance makes a lot of sense because something that inaccessible needs to stand on it’s own. I also wanted the opportunity to add more smart home features over time.