Short answer right now; no. Currently, Sunset can only help you search for one person's financial accounts at a time. If you signed up to search for your grandmother's accounts, for example, you won't be able to also search for your grandfather's accounts within the same Sunset account.
We know this can be inconvenient, especially for families dealing with multiple losses. We're working on adding support for multiple searches in the future.
If you need to search for another person's accounts, the best workaround right now is to have a different family member who is related to that person sign up for their own Sunset account.