Thanks for all the responses!
It looks like a newer Lionchief train set would be best for the kids interests as of now, maybe I’ll pick up some older stuff just for me.
I did order some new traction tires for the MP15, and am trying to find some maintenance instructions for it also.
For the other steam engines, one is a Lionel 8902 designed to run on DC. It didn’t operate very well, and I’m not really attached to it so I may just keep it for display.