Yeah, I agree with agz that a genuine personal note is the way to go regardless of what you may decide to include as a gift. And the note has to be genuine, not some corporate crap.
And here's an idea for a part of your gift package. Caramel apples from The Apple Gal. Well, really much more than caramel apples as they have countless varieties. The owner is an Ag. She just went brick-n-mortar a few months ago. Don't know her, haven't been to her shop(yet), but she's killing it.
https://www.facebook.com/watch?v=1570276737076805And so you pull together a package that includes a well thought out personal note(don't write the same one to all 4 because I promise you they will compare notes), a tabletop bonfire and a couple of apples. Make it a family theme, include a link to Apple Gal's story.
I could go on, but whatever you write or do, you gotta mean it. And I believe you do, otherwise you wouldn't have asked the question.
.