Your first cousin's aunt may be your mother, or another of your aunts (sister of either your mother or father) or may not be related to you at all. The latter situation occurs if, for example, the cousin is related to you through the brother of your mother, but your cousin's aunt is related through the brother's wife.
Your great aunt's daughter's children (her grandchildren) are your second cousins.
Your aunt's sister is either your mother or another aunt. Therefore, her children are your cousins. If her sister is your mother, then those children are your siblings. If she is another aunt, then they remain your cousins.
That's easy cousins.
If the great grandmother of A is the aunt of B's grandfather, then A and B are third cousins.
Your son and your aunt's son are first cousins once removed to each other.
Your aunt's children are your first cousins and theirchildren are your first cousins, once removed.Your children and the children of your first cousins are second cousins to each other.
Your son and your mother's sister are in a "Great Nephew/Great Aunt" relationship.
Your aunt's grandchildren would be your first cousins once removed, as the your aunt's children are your first cousins.
They are of no blood relation. But they are cousins by marriage or 'step-cousins' as such.
Cousins.
You're using a couple of vague terms there. They're probably your "cousins" also, but it's possible they're "no particular relation".I'm going to use the male terms throughout just to save typing. Take it as a given that when I say uncle, I really mean "uncle or aunt", when I say father, I really mean "father or mother."It's kind of weird to ask about your uncle's cousins, because if they're your uncle's cousins, they ought to be your father's cousins too. Unless you mean "uncle" as in "your father's brother's husband" (hey, I did say male terms throughout), in which case his cousins are basically "no relation" to you.However, your father's cousins are your cousins also, except "once more removed" from whatever they were to your father.If they were his first cousins, they're your first cousins once removed. And so on. It does get a little tricky, because your father's first cousins once removed could either be your first cousins twice removed, or your second cousins, but "how do you determine exactly what kind of cousins two people are" really deserves its own separate question.
Your daughter and your sister's son are first cousins to each other. Your sister's son's daughter (her granddaughter) and your daughter are first cousins, once removed.