If the matter is as you have described, your breastfeeding from Fatimah does not make you unlawful to her sister, because you were eight or nine years old.
The period of breastfeeding that makes marriage to foster-siblings unlawful is the first two years of the infant's life. Allah (Exalted be He) states:
The mothers shall give suck to their children for two whole years
Therefore, this does not affect your marriage. (Part No. 21; Page No. 48) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.