Does a wet nurse become an aunt to her sister's son through breastfeeding, and is it permissible for her to uncover herself in front of him, and does she become an aunt to the children of her sister's daughters through breastfeeding?

Suckling prohibits what lineage prohibits. Thus, whoever suckles from a woman five full sucklings becomes her son by suckling, and her children become his siblings. If your eldest maternal aunt breastfed your youngest maternal aunt five sucklings, then the children of your youngest maternal aunt become your mahrams, and it is permissible for them to see from you what a man sees from his mahram women.