Michael, I can empathize with you on how diabetes has affected you. I know that all too well myself. You have gotten some real good info here, especially from Steve. The only thing I can add is that you were going in the right direction, you do need to add more weight, though.

What would benefit you more would be what is called endurance training. That consists of doing lighter weight for a bigger number of reps in a set. You probably want to shoot for at least 15 reps in a set for three sets. The best way to tell if you need to add weight is the ease you have doing this. If you can do all you reps in all three sets fairly easy, you need to add more weight.

I would do the leg curls and leg extensions on the machine and the squats. The squats will actually work both the hams and quads fairly equally.