It’s a difficult one. Sometimes I’ll help assist a passenger in putting a bag up, if say they’re elderly or frail but other than that I work on the ‘you pack it you stack it’ rule.
If you can’t lift your bag into a locker then don’t pack as much, or check it in.

With regards to exit row capabilities, these should be assessed by the crewmember responsible for doing so once boarding is complete. Obviously if I don’t think a pax is capable of operating the exit; or doesn’t understand the instructions then I’ll move them. It’s not worth the risk. Most of the time, though, they’re GCHs who have sat there hundreds of times before and know exactly what’s required.