Your ankles are weak thus easy to sprain. They may just be the weak point of your lower body. However, my ankles have always gotten sprains very easily versus any knee/hip issues.
The one leg balancing stuff is good. SLS/pistols can be good if you can into them but working them with the free leg hanging is pretty good.
A simple way to avoid this is a LOT of ankle circles and heel/toe raises with feet straight in front, turned out and turned in. I mean a lot. Build up to three digit numbers for each position. Basically a lot of low intensity volume.