For heavy back squats, you can substitute front squats, Zercher squats or, as I'd recommend, Bulgarian split squats. With Bulgarian split squats, you can do them with dumbbells or kettlebells in hand, with a bar in the Zercher of front squat position or, because you won't be using large amounts of weight, with the bar on your shoulders as for a back squat.
Lunges will train your posterior chain nicely instead of deadlifts, and you can also use Romanian deadlifts (stiff-legged deadlifts). Do them slowly, with a low weight.
For heavy back squats, you can substitute front squats, Zercher squats or, as I'd recommend, Bulgarian split squats. With Bulgarian split squats, you can do them with dumbbells or kettlebells in hand, with a bar in the Zercher of front squat position or, because you won't be using large amounts of weight, with the bar on your shoulders as for a back squat.
Lunges will train your posterior chain nicely instead of deadlifts, and you can also use Romanian deadlifts (stiff-legged deadlifts). Do them slowly, with a low weight.
Don't hesitate to ask, my friend.