We think that two important points ought to be tackled: 1. Number of suckles that prohibits marriage. 2. Islamic view of marrying cousins.
Tackling the first issue, we would like to stress that according to the Hanbalis and Shafi`es, the marriage become prohibited by 5 suckles that are known and saturating for the baby. This fact is supported by the Prophetic hadith in which the Prophet (peace and blessings be upon him) is reported to have said, “One suckling or two can’t be considered a prohibition (i.e. of marriage). Thus, according to the majority of Muslim jurists with the exception of the Hanafis, you are originally permitted to marry your cousin in case his mum has breastfed you less than 5 suckles. In case the number is five or more, then it is prohibited for you to marry him.
Our advice for is to make sure about the number of suckling before taking any decision and fear Allah Your Lord.
As for the issue of marrying cousins, we can say that originally Islam permits marrying cousins, although it is preferable to choose a marriage partner from outside one’s family. This is because Islam is generally keen to widen the circle of social bonds. As for the fear of hereditary diseases in case intends to marry a cousin, it is a good practice to have a blood test before marriage. If one suspects some hereditary disease or any other problem then he/she should seek the advice of a medical expert in this field.