You can group taxpayers together by prefilling the taxpayer information and then sending each of them your link to eSign for their own records. Please see this video for an overview.
If you prefer for the taxpayer to complete all the information, then you can use the search bar to find taxpayers with the same last name.
Enter a searchable term in the Client Number field for taxpayers with different last names. Next time you search, both will appear in your list.