I have sympathy for your position, it sounds like you're trying to do the best you can for vulnerable people in a capitalist system.

Under this system the only way you can retire is to have an income unrelated to work. Because we can't remove ourselves from that system, one day you'll have a choice to make. It may be worth exploring novel options like transferring ownership to the tenants, having rent increase limits written in to the contract for sale, etc, but the practicality of these are likely very limited.

This is why capitalism is so pervasive, because the best financial decision you can make is the one which furthers exploitation.

There isn't really a good option tbh.