What is the ruling on marrying a woman whose aunt and uncle were breastfed by my mother, knowing that she is both my maternal uncle's daughter and my paternal aunt's daughter, and does intermarriage affect the health of children as has been said by some jurists, and do you advise me to marry her or to seek someone else?

There is no objection to your marrying this woman. Your mother's breastfeeding of this woman's maternal aunt or paternal uncle makes them your siblings through suckling. This does not affect the permissibility of your marriage to her, as she falls under the general meaning of His Almighty's saying: "And lawful for you are those beyond that." Furthermore, marriage to relatives is permissible in Islamic law, and what medical professionals mention about its effect on the health of children is a rarely occurring matter.