Is it permissible to marry the daughter of the elder maternal uncle, while having been suckled by the grandmother along with the younger maternal uncle?

What is established by suckling is established by lineage, and the suckling child is the one for whom kinship is determined. If the grandmother was the mother of your oldest maternal uncle, or if her milk was for his father, then you become his brother by suckling, and it is not permissible for you to marry his daughter, because you are her paternal uncle by suckling.

However, if the grandmother was not the mother of your oldest maternal uncle, and the milk was not for his father, and you did not share suckling with him from another woman, then it is permissible for you to marry his daughter, unless another cause of prohibited kinship is established between you.

The suckling that prohibits marriage requires five full sucklings within two years.