RE: How do you name Family relationship?
I just tried the relationship calculator and couldn’t do your family, however I will do my best.
your sister’s daughter is your niece so her husband would be your nephew-in-law.
To your father, your daughter-in-law would be his grand-daughter-in-law, and your sister’s daughter’s husband would be his grandson-in-law.
English and maybe all languages are tricky about relationships. I wish there was a word for the relationship between me and my daughter-in-law’s mother.