It depends on their age. If they are in their early teens they are most likely non-mahram to your mother and your maternal aunties since most boys by around this age grow sexual awareness, and therefore they should observe most if not all rules concerning mahram-non-mahram relations. But they are mahram to their maternal and paternal aunties, that is the sisters of their parents, but not to their aunts-in-law. This aya of the Holy Quran enumerates the mahrams of a women.
And say to the believing women, that they lower their gaze cast down
their eyes and guard their chastity, and do not reveal their adornment
except that which is outward (face and hands); and let them draw their
veils over their neck, and not reveal their adornment except to their
husbands, or their fathers, or their husbands' fathers, or their sons,
or their husbands' sons, or their brothers, or their brothers' sons,
or their sisters' sons, or their women, or what their right hands own,
or such male attendants having no sexual desire, or children who have
not yet attained knowledge of women's private parts; nor let them
stamp their feet, so that their hidden ornament is known. And, O
believers turn to Allah all together, in order that you prosper.