I would probably not write a letter. I like the previously suggested idea of an introduction via Zoom or something like that. Most kids are used to talking with people on screens, especially because of the pandemic.
Don't try too hard. Just be pleasant. Keep it low-key and see where it goes. Let Grandpa lead the way on this one. It is most likely that the parents will have the biggest influence on the family relationships anyway.
And -- about that. . .
Please forgive me for the intrusiveness of what I am about to say here -- and I really do
not want you to answer about this because it is absolutely none of my business, and it is not something you need to tell a bunch of strangers on a forum. . .
A prenup can be really important at this point in life when people usually bring assets into a later marriage. A prenup does not need to require that one would be willed nothing when the other one dies, but a good prenup can make things work out fairly for the couple and also for the family. I know a prenup is not the most romantic thing to talk about, but could be practical, especially when there are potential heirs from previous marriages.
Prenups are not just for the fabulously wealthy. They can cover a lot of details like "yours, mine, and ours" and stuff about the house, etc.
I can still hear a friend of my parents who had been widowed twice and was thinking about marrying for the third time at a rather senior age.
She was telling us about her second husband and said, "His family was always wonderful to me. They liked me. We had one of those. . .oh, you know what I mean. . .one of those things from our lawyers. . .I can't think of what they're called."
I answered, "Prenup?"
"That's it," she said, "and I am getting another one this time around."
Smart lady.
Boomer