I'll offer Pilates for exercise but to lose weight reasonably quickly it's diet. I'm no fan of diets (because they're "temporary behaviour" and there's always a temptation to go back to bad stuff when they're over! and put the weight back on) so one solution is to cut down the portion sizes maybe by 1/4 at first then 1/3 after a couple of weeks - and try not to eat between meals.

ANY reduction in the weight off one's feet and knees is good.

Good luck.