Your great grandfather's sister is your great great aunt. You are her great great niece or great great nephew, depending on your sex.
Your grandfather's sister's children are your 'first cousins once removed'.
Your husband's sister is your sister in-law.
The relationship between the families of inlaws is similar to the relation ship with their family members. For example The relationship of my brother in law(sister's husband) and my another brother in law (wife's brother) will be simmilar to those relation ships with their brother's family.
How could the relationship between Pip and Biddy be described?
The legal relationship with your sister-in-law is that she is the wife of your brother or the sister of your spouse. That does not give you any legal rights in her life or her any legal rights in your life. It does mean that you are both part of an extended family, but that is more cultural than legal.
Your grandfather's sister is your great aunt.
nothing
They are Brother & Sister.
Your brother's wife is your sister-in-law. The English language has no relationship term for the brother of your sister-in-law. He is not considered to be related toyou, although he is your brother's brother-in-law.
Your mother's brother is your uncle. Your uncle's wife's sister is his sister-in-law. There is no family relationship between you and your uncle's sister-in-law's daughter, unless the sister-in-law is married to someone who is related to you.
Your great grandfather's half-sister is your great great aunt, the same as his full-sister is.
If you have a good relationship with your family members, then nothing is worth breaking that relationship for. She could be jealous of your sister and have possessive tenancies in a relationship. If you are quite early into you relationship with this girl, then you should seriously think about what is important. If you break relations with your family members, then who is going to help pick up the pieces if your relationship doesn't work out. After all you cannot get better support than family.