Duplicate guardians can occur in the same way as for students - when a student is enrolled in a Shared Teaching course, but has an existing profile on the teaching school's site.
It can also occur if a Shared Teaching student has a sibling attending the teaching school.
In this scenario, both profiles need to be kept, as the data is managed by separate schools - the Shared Teaching student's guardian on the home school site, and their sibling's guardian on the teaching school's site.
As such, it is not possible to merge these guardian profiles.
Top Tip: Guardians won't be able to sign into the duplicate account - more details here: Which Shared Teaching site should guardians log into?