Yes, your brother-in-law is your relative by virtue of marrying your sister, of of you having married one of his siblings. But he is your relative by law, not because you have common ancestry. So that relationship can go away - if there is a divorce, for example.
Yes, your husband is considered to be your closest relative.
Yes, a cousin-in-law is considered a relative by marriage, not by blood.
SHe's your relative by virtue of her sister being married to your brother.
Before or after a divorce a step-sister is not considered a legal relative in most jurisdictions.
Unfaithful, a cheater and many other names that are inappropriate for me to say on this website.
If by "stepson" you mean someone who was legally adopted into the family - yes, they are a legal relative. However, they are NOT considered to be a "blood" relative.
Brother in law means is translated to SAALA in hindi. However saala is also considered to be abusive language so better not use it.
Yes, your wife is a relative by marriage, and is considered to be your closest relative.
Yes, she is your sister-in-law.
A relative's business address
The phylum Chordata is considered to be the closest relative to humans. Within Chordata, the subphylum Vertebrata, which includes animals with a backbone, is the most closely related to humans.
If they have a biological relative then no, a brother is a closer relative than an adoptive father is. Legally though, if you are the only guardian/ relative then you will be next of kin.