We have a complex-families tag for:
Multiple marriages, step children, adoptions and other extended family scenarios
and it has a tag wiki:
The notion of the family extends beyond that of a single union and their offspring. Extended relationships, though, can be complex. Use this tag to mark Q&A that is specific to the notion of these extended, complex family scenarios.
If you need to find the English-language term for the relationship between two members of a simple or complex family, the Steve Morse relationship calculator will help.
It was used today on Incestual representation in genealogy tree.
As something of a catch-all tag, is it needed?
We currently have a separate tag for adoption.