Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The men who can see a woman without the covering of her head are her Maharims: her family kin her suckling relatives and the people related to her by marriage.
Her family kin are: the fathers and grandfathers (and great grandfathers) whether they are from paternal or maternal side, and the sons and grandsons, the children of daughters and their grandchildren.
The brothers from the same parents, or the brothers of fathers and mothers, and the nephews and nieces from the latter three categories, and the paternal uncle, or the uncle from the father’s or mother’s side, and the maternal uncle from father’s or mother’s side are all Maharim as well. And the Maharims like the aforementioned from the suckling relations, as the Prophet (Sallallahu Alaihi wa Sallam) said: The people who are Maharim from the suckling relations, are exactly the same lineage of relations from the family kinship. [Reported by Bukhari and Muslim]
The Maharims from marriage are the children of the husband and his grandchildren, either his own sons or the sons of his children either males or females, and the fathers and grandfathers of the husband from father’s or mother’s side.
And also the husbands of daughters and granddaughters, and the husband of one’s mother on the condition that he has already consummated the marriage as Allah Says (interpretation of meaning): {…your step daughters under your guardianship, born of your wives to whom you have gone in - but there is no sin on you if you have not gone in them (to marry their daughters), - ….}[4:23].
Allah knows best.