Hi PJ. I hope you find weight training very rewarding. My thoughts on your situation are, don't worry about what weights you use, just go through the motions of the exercises that do not cause joint pain. As you know, your body is adding to any weights you use. I wouldn't worry about squats or lunges for a while.

I would suggest more along the lines of:
*Sitting in a chair leg extensions, no added weight, for quads. Together or singles, whichever feels best.
*Standing, holding onto your power rack and bending your knee lifting your heel towards your behind for hamstrings.
*While in the "holding on" hamstring position do some side leg raises, then leg crossovers. Those work abductors and adductors.


Now if I've misjudged your abilities then please disregard those suggestions. My point is for you to start off with useful exercises that shouldn't be hurtful ones for you. If you feel any pain in your joints, stop. Do not try to push through pain. NOT helpful.