Similar advice here my friend.

I have limited range for full squats.

In my work outs I’m using as heavy a weight as possible where I can keep form for as long as possible.

My ‘tunnel’ for the squats especially, is shorter than it should be as I can’t attain the stable bottom position. So I work within my tunnel, and come back up once I know my form will break if I descend any lower, then when working on mobility I try to extend the tunnel, but this is going to take time and patience.

I would apply that to all your movements – work in range, with as heavy a weight as possible that will allow you to keep that range, and progressively overload from there. That weight could be additional, it could be simply body weight, or it could be assisted body weight. Whatever works. Be careful though, it’s trial and error to find out what weights are your work out weights, start light and build, and stop once it begins to feel like too much. Trust your body and the inherent wisdom it has.

stay persistent.