Is four sucklings considered sufficient for the the maternal aunt to become a mahram, especially given the differing jurisprudential opinions regarding the number of sucklings that establish mahramiyyah?

The authoritative view for us is that the number of sucklings that establish a prohibitory relationship (mahramiyya) is five. Anyone who suckles less than that must treat the woman who suckled him and her daughters as non-mahrams, because they are not mahrams to him. There is no blame upon one who believes in theilience of the prohibition with three sucklings if she uncovers her hair in front of him, for there is no denunciation in matters of scholarly disagreement.