Who are the blood-relatives with whom kinship ties should be maintained?
Blood-relatives are those from the side of one`s father and mother: grandfathers, grandmothers, uncles, and aunts.
Is it permissible for us to sever ties of kinship if our blood-relatives` gatherings involve acts of sin?
Maintaining kinship ties is mandatory, thus if visiting your blood-relatives hinders their sinful acts , then you should do so. However, if their sinful acts persist while you are at their gathering, then it is sufficient that you maintain kinship ties via telephone and the like.
What is the ruling on a woman shaking hands with the brothers of her husband`s father, and not putting on Islamic wear before them?
The aforesaid are strangers to the their brother`s son`s wife, therefore, it is forbidden for her to take off her Islamic wear before them, or to shake hands with them.
Is the maternal uncle of one`s mother a Maharam?
All perfect praise be to Allah the Lord of The Worlds. May His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Mother`s maternal uncle is a mahram. And Allah The Almighty Knows Best.
* In Islam, a mahram is a member of one's family with whom marriage would be considered haram, concealment purdah, or concealment of the body with hijab, is not obligatory; and with whom, if he is an adult male, she may be escorted during a journey, although an escort may not be obligatory.