How To Write A Family Reunion Letter Samples . The name of your event and the purpose, which, in this case, is a reunion. Understand what elements make up a great reunion invitation so you can apply them to your design. Sample Family Reunion Letters from gatheredagain.com More than 200 guests have. This is the letter that you will use initially to send out to family, informing them of the family reunion planning that is in process. In this letter, you will include all of the details known at this point, along with contact information for the family member (s) in charge of the planning.