You have to replace the COD with a pronom personnel COD (me, te, le/la/l’, nous, vous, les) en the COI with a pronom personnel COI (me, te, lui, nous, vous, leur)
So the first one will be: Vous les leur rendez. Because vos devoirs is the COD and will become les and à vos professeurs is the COI and will become leur.
I hope you understand this and you’ll manage to solve the rest by yourself. If needed I can solve the other questions for you too.