Took me a while to do both, Juno. The second time, I went through home PT, outpatient PT and then contracted a personal trainer to help me integrate PT exercises into my regular workout routine.
Lunges were left to the last, I'd say non-weighted lunges I started to do about five months in. There's a stance in martial arts which is like a lunge, not exagerated, but there is a whole mechanism for moving from one to the next. I was using that to do my 'lunges'.
It helped that early on (late home PT) one of my stretches was to put one foot flat on a chair while standing in front, using the chair to balance if needed and hold it there. That helped - the chair was not high and I only did it when flexible enough to reach properly.
I think that helped my later lunges, but also remember that I had no 90 degree or other restrictions.
Squats, I did chair squats without weights at about four months, real squats without weights about seven or eight months in.