Can the father refuse to give his daughter in marriage to a young man who is good in terms of character and religious commitment, because his parents are not Sunni?
Question

My father and I do not have a good relationship, because his wife does not like us, and he has been unfair to us in all ways. A while ago I got to know a family, all of whom follow are Sunnis, except the mother and father, who follow a different school of thought. The children are all good in terms of religious commitment and character, and one of the sons has proposed marriage to me. I had no choice but to tell my father, so that he could give me in marriage, but he refused, because the mother and father do not follow our school of thought, but the suitor does follow my school of thought. My father did not do that out of concern for me; rather he said that his reputation would become tarnished if people found out. I want to marry this man, and he is a suitable match for me, because he is religiously committed, of good character and wealthy. Is the school of thought of the mother or father of the suitor a valid reason for refusing to let their son marry me, or does my father have no right to reject him? Please note that he is a righteous man and I want to marry him.
Praise be to Allah.If the father refuses to give his daughter in marriage to a young man who is of good character and religiously committed because his parents are not Sunnis, then his rejection is valid, and is not regarded as preventing his daughter from getting married, because marriage is a strong bond between the spouses and their families. Her father will have no choice but to interact with the father of this young man, and his parents will become grandparents to your children. The fact that the parents follow a path other than the Sunni path is most likely to bring shame on you, your family and your children, and there is the possibility of conflict and dispute in the future. So your father is not to be blamed for rejecting this marriage.
No matter how estranged the father is from his daughter, his paternal compassion will prompt him to make a good choice for her.
If we assume that his concern is for his reputation only, he has the right to be concerned and not agree to a marriage that will tarnish his reputation or undermine it. Hence Islam gives weight to the matter of compatibility between the spouses, and gives the right to all the guardians of the woman to reject a marriage to one who is not compatible, because the shame will affect all of them.
It says in Kashshaf al-Qina‘ (5/67):
Compatibility is the right of the woman and of all the guardians, whether they are closely or distantly related to her, and it is even the right of guardians who may be born after the marriage contract has been done, because they will all be shamed equally if there is no compatibility.
If a one’s marriage is arranged to someone who is not compatible with her, then anyone who is not pleased with the marriage has the right to nullify it – including the woman and any of her guardians – who may express their disapproval immediately or later on, because the option to nullify is there due to shortcomings in the one with whom the marriage contract was done. This is akin to the option of proceeding with a sale transaction or cancelling it. The more distantly-related guardian has the right to annul the marriage with the approval of the one who is more closely related, and with the approval of the wife, so as to ward off what the more distantly-related guardian could face of shame.
So if the father gives his daughter in marriage to someone who is not compatible, with her consent, her brothers can nullify it – as stated – because they will all carry the burden of shame resulting from the marriage of a female relative to someone who is incompatible. End quote.
Conclusion:
The difference in schools of thought is clearly a shortcoming in the family of the suitor, and it may bring blame and shame on you and your family.
Or it may not lead to that in some places and some communities. But if the father rejects the marriage for this reason, then his rejection is valid.
And Allah knows best.