The first is copying the groupings from the template into your own word processor, sharing it directly with your couple, and having them fill in the names of their family members. Using a shared document of some form means they can make their own changes online.
The second is creating this list for the couple. Prior to the wedding, ask the couple for a list of their immediate family members so you can create a custom list.
We do this in our wedding questionnaire when we ask for other important wedding information a few months before the wedding. We ask the couple to list each family member who will be present during immediate family portraits (usually parents/guardians, siblings, & grandparents). If necessary, we also ask them to also clarify their relationship to the couple in parentheses, for example, Alex (sister-in-law), Eric (step-father). We just have them skip any that don’t apply.
Either way, we recommend having the couple review the list make any additions/subtractions or adjustments and approving the document before their wedding day!