Does the questioner bear sin if she allows her younger brother (9 years old) to play "Minecraft" and "Zombies" on her phone, given the suspicions surrounding their inclusion of polytheistic or forbidden matters such as the presence of the cross symbol, and the words "hell" and "vow," and what is the ruling on the mother compelling the questioner to allow this?

The aforementioned game is forbidden (haram), and it is not permissible to allow children to play it, lest they become accustomed to it and their minds be corrupted by its misleading beliefs and scenes. It is not permissible to obey the mother in giving the device to the brother to play this forbidden game, based on the saying of the Prophet, peace and blessings be upon him: "There is no obedience to a creature in disobedience to Allah." And the mother's statement "the sin is on her" does not absolve you of responsibility. You should be gentle with your mother and try to convince her of the game's impermissibility and its danger.