I don't know the AA program and lounge benefits at all, but if you have access to the arrivals service in T3, then clearing immigration @ T3 and going upstairs to the lounge would be a good time killer. If its anything like the UA arrivals, there are nice shower suites and a so-so array of breakfast goodies (I'd wait to eat until BA).

If not "terribly mobile" means they can still take a leisurely walk with moving walkways for part of it, I'd then walk to T1. If its too far to walk, I don't know what kind of inter-terminal transport there is landside. With that kind of connection, however, and given how crappy it can be to take the bus T-3 T-1, and given all the time you have, I'd walk.