On the Estimate sheet, you can see that the Group Name has been inserted on top,
I don't see this on the uploaded workbook so I don't know what you are looking for here.

and finally there's a formula to sum the total amount of that specific group.
Until the first one is in place above, then I don't see how to do the second one.

Do you want the Group Name to come over with the other data, and then do a SUMIF calculation by group?