What is the kinship relation between us and the remaining children of the maternal aunt if our grandmother breastfed two of the maternal aunt's children, and is it permissible to marry them?

Your maternal aunt's children who were not breastfed by your grandmother are not your milk-uncles, because the effect of their brothers' suckling does not extend to them. Rather, it is limited to your maternal aunt's two sons who were breastfed by your grandmother.