Is the son of the maternal aunt, whom one wishes to marry, considered a maternal uncle (khal) and a forbidden (mahram relative) if the mother was breastfed by his elder brother?

If your mother breastfed with your cousin (her aunt's son) who proposes to marry you, then he is your maternal uncle (khal) through breastfeeding, and it is forbidden for you to marry him due to the prohibitory degree established by suckling. However, if your mother did not breastfeed with him, but rather breastfed with his brother from his mother's side or from another woman who is not his mother, such that he (the proposer) was not breastfed by her (your mother) and her (the proposer's mother) is not a blood relative (of your mother), then he is not her brother through suckling. In this case, it is permissible for you to marry him, as there is no prohibitory degree between you two.