If your parents live separately and both want to log in with their own login data, you can set this up using the deputy feature.
How does the whole thing work?
A small example based on "Max".
Invitation:
1) Max is currently managed by himself or a parent e.g. (dad).
2) Max shall be additionally managed by another parent (mom).
3) The current owner (Dad) goes under "Settings" to " Deputy" and creates an invitation with the label of the respective name. Here for example "Mom".
4) It shares the appropriate invitation with the deputy, which is to administer in the future with.
5) The deputy now logs in with his own mail address and password. In our example, Max's mom is now logged in with her own login data and can now perform all actions on behalf of Max.
If you want to know how to remove a deputy, please have a look here.