Yes, your husband is considered to be your closest relative.
In English there are no masculine or feminine forms. English uses gender specific nouns for male or female.The noun 'uncle' is a singularnoun for a male relative.(Although your uncle himself is, probably, masculine.)The corresponding singular noun for a female relative is aunt.
Your uncle's wife is your aunt.
how many people live in Vietnam
That's actually determined by state law. But usually it would be the closest blood relative an adult sibling if applicable, followed by maternal grandparent(s), paternal grandparent(s), aunt or uncle, and so forth.
Yes, your wife is a relative by marriage, and is considered to be your closest relative.
cousin, niece, nephew, aunt, uncle, grandparent
A common gender nouns for uncle are relative or family member.
uncle, niece
Yes, you and your great uncle are descended from the same people, two of your great great grandparents, so you are biologically related, but for most purposes you are not "close relatives."
uncle
Yes! He is your uncle.
Uncle
Grandparents are usually considered to be immediate family only if you are living with them. Of course, as your parents, they are your immediate family.
a dungong
If you and your brothers are you uncle's only living relatives, then you are the most immediate family.
She'd be your second cousin; your uncle's daughter would be your first cousin.