Is it permissible to marry a girl who was nursed by her paternal grandfather, knowing that she was not nursed by her mother or paternal aunt? And is nursing from the grandfather considered a barrier to marriage?

If you were suckled by your grandfather's wife five known sucklings, you become a maternal uncle to your paternal aunt's daughter through suckling, and it is not permissible for you to marry her. However, if the number of sucklings was less than five, it is permissible for you to marry her, because less than five sucklings do not establish prohibition. The proof for this is what 'Aisha, may Allah be pleased with her, narrated: "Among what was revealed in the Qur'an were ten known sucklings that make marriage unlawful, then they were abrogated by five known sucklings. The Messenger of Allah passed away while these were among what was recited from the Qur'an."