Is it permissible for me to marry my maternal uncle's daughter, knowing that I was nursed by my grandmother (my maternal uncle's mother), and that my maternal aunt is my mother's sister from her mother only?

If you breastfed from your grandmother — your aunt’s mother — five full feedings before reaching two years of age, then your aunt becomes your sister through suckling, and therefore, it is not permissible for you to marry her daughter; because she becomes the daughter of your sister through suckling, due to the Prophet’s (peace be upon him) saying: "Indeed, suckling prohibits what birth prohibits."