All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.

If you were breastfed from great grandmother then all of your aunts takes the rulings of your sister as regards marriage, besides you aren't permitted to marry their daughters as well, due to the fact that they became your foster nieces which entails that you are their uncle. In this regard, The Prophet (PBUH) said (What means): "What unlawful by reason of suckling relationship is unlawful by reason of blood relationship." [Agreed upon]. And Allah Knows Best.