Is it permissible for someone who was not suckled by the grandmother to marry, if the grandmother suckled some individuals from three families (the questioner's household, the maternal uncle's household, and the maternal aunt's household), or have all three households become forbidden to one another due to suckling?

If your brother, sister, and maternal cousin were suckled by your grandmother five times or more within the first two years of life, they become your milk-siblings. Consequently, marriage with the sons and daughters of your grandmother and their offspring becomes forbidden due to the milk-kinship, in accordance with the hadith: "Indeed, suckling prohibits what birth prohibits." However, for those who were not suckled by your grandmother, this prohibition does not apply.