Yes, your husband is considered to be your closest relative.
Yes, the husband of your wife's niece is a remote relative who might be described as a nephew-in-law.
Yes. Your sister-in-law's husband is your brother.
in fact yes. lets say you're nice is you're sister, so when she married that would mean that her husband was consittered you're brother. let me just say im only a kid. im only under 12. and you know...
Yes, she is your sister-in-law.