spouse
mate, spouse, groom
The neutral term for husband and wife is "spouse." This term is inclusive and applies to any partner in a marriage or committed relationship, regardless of gender. Another term that can be used is "partner," which also reflects a more neutral and modern approach to describing a significant other in a relationship.
No she doesn't have another husband.
The term for "husband" in Yoruba is "ọkọ."
it would be step brother in law.
If your husband wants to watch you with another man, then there's a problem. No husband should want their wife with another man let alone watch them.
If you mean the feminine equivalent of husband the word you are looking for is wife.
spouse means husband or wife.
The English language has no specific term describing the relationship between a wife and her husband's grandmother. If you absolutely require something other than "my husband's grandmother" you could try "grandmother-in-law." However, that term is neither widely used nor accepted.
Widower
Your sister's husband is your brother-in-law. It does not matter whether you speak of your elder sister or another sister, the same term is used for the husband of any one of your sisters.
The Bradley method uses the term "husband coached" childbirth. Most other forms of childbirth methods have some term for husband or coach/support person.