Covering head with dupatta

Sorry to say in say nikah karna mana hai per maharam naheen ho jaatay.

Where in quran or hadith it says that father in law and mother in law are mahram.

You can hence prove that they are mahram because they can’t have nikah.

Nikah karna to kisi ki biwi say bhi kisi mard ka mana hai to is tarha koi ghair aurat kisi ghair mard kay liaay mahram naheen ho jati jub tuk wo kisi aur ki biwi na ho.