Should nail polish be removed before making ablution?
Yes, it should be removed because it prevents water from reaching the nails.
Is it permissible for me to eat from the animal that I slaughtered for Allah to protect my family?
It is permissible to eat from the non-vowed animal sacrifice, and the person is rewarded based on the amount of meat that he had given to the poor. However, there is no evidence in Islamic Sharia indicating that slaughtering an animal protects one`s family, but it is a way for thanking Allah, The Almighty, for his grace.
What is the ruling on the existence of cattles' marketplace of (Sheeps, cows and chickens ) inside a graveyard?
Graves must be respected, and it is not permissible to sit on them or show any disrespect. Establishing a marketplace within a cemetery is undoubtedly a form of disrespect to the deceased and is not permissible. Such actions should not be tolerated. And Allah Knows Best.
Is it permissible to give lessons to mixed students of the seventh grade?
It is impermissible to give private lessons to mixed students since such an act leads to serious consequences for the students in this grade are teenagers.