Is it permissible to marry the sister of one's paternal uncle's wife if the paternal uncle's wife breastfed the questioner a varying number of times (five or fewer) until satiation, and the breastfeeding occurred in front of the questioner's mother, who affirms that it did not exceed two or three times?

The prohibited suckling consists of five known sucklings, and doubt about the number does not establish prohibition. There is no legal impediment to marrying that woman unless it is confirmed that you nursed from her sister five known sucklings. As a precautionary measure, it is permissible to avoid her, as many scholars hold that little and much suckling are the same in establishing prohibition. This is the view of the Maliki and Hanafi schools, and it is more absolving for one's conscience and further removed from doubt.