I would start off with Joinup
She is gimpy bc she has a bad hip and is a 16 yr old that was rescued bc she was going to the slaughter bc she was " good for nothing other than dog food"😬 some ppl man I can't stand some of them
figure out why the one is gimpy then just start from the top. treat them like they've never been handled before.
I agree with Alexis. Don't feel like you have to rush. Take your time and get the basics down first
Personal i would start with ground work and see what happens. But if there good then you could try riding them but by careful