Must I clean and burn the books placed on the roof of the house by family members, after I have done so previously and warned them against leaving them exposed to bird droppings, or is it sufficient for me to warn them again and they bear the responsibility for them?

It is not permissible to place anything containing the ذكر الله (remembrance of Allah) in a disrespectful place, and books containing the remembrance of Allah must be protected.

If you find neglected books or papers containing the remembrance of Allah, you may dispose of them by burning or burying them in a clean place, provided that this does not cause hardship.

You are not required to search for papers everywhere, but if you see a verse or a hadith, you should pick it up. You should also gently advise relatives about this matter.