Is it permissible for my uncle to marry a girl if he is in doubt and confused about whether he was nursed with the girl's younger sister?

If the paternal uncle did not suckle from the woman he wishes to marry, or from her grandmothers, then he may marry her. She is not forbidden to him merely because he suckled with her maternal aunt, provided that the suckling occurred five times or more with certainty. It should be noted that suckling is not established except with certainty.