There are some very good guides to legacy letter writing. You can find these with simple on line searches. Some of the sites are listed below.
The literature does not focus specifically on letters to great granchildren that have in turn matured to become grandparents themselves.
Nevertheless it is probably fair to say that there are generic elements that you may like to include in your own letter if you are trying to encapsulate the main experiences of your life to date.
There is certainly agreement on one key point in particular. There is NO single "right way" to write a legacy letter.
1) This is your letter principally about your life and is best framed in an idiom that best suits you. It would be banal of course to suggest that a poet should write a poem or a gambler wager a particular spectacular bet on the future but the overall message is clear. It is enough to just be yourself.
2) When a recipient (your great grandchild on our site) receives a letter from you this will almost certainly bring excitement and happiness and a sense of gratitude that you took the time and trouble to communicate between generations of your family all those years ago.
So, in summary, there are guides and you may find them useful. Some include elaborate tool kits. These may be ideal for some writers but not others.
When we wrote our legacy letters we thought that the task would be lengthy and difficult.
We were wrong as we found it fairly straightforward and enjoyable.
Reviewing the experience of writing our own letters indicated that Paul wrote mainly in "stream of consciousness" perhaps lacking a bit in organisation. Carol, by contrast, built her story through first forming an outline autobiographical structure of bullet points, brick by brick building to a conclusion. Our Dad, Alec Mitchell (and Great Grandad of six) who sadly died on 9th March 2015 approaching 90, had help with his letter principally through the medium of a lifestory family photograph album from his childhood through retirement. Three distinct approaches in one family!
We think that, like us, you will be very pleased with the outcome once you have actually written your letter, confident in the knowledge that it will be delivered by us to your great grandchild.
* www.personallegacyadvisors.com