Try Briar.

But in our defence we fly alot.

And Alot is very proud of your frugality.

Make sure everybody owns a a Nintendo DS, then load up Pictochat.

https://briarproject.org/

I know you’re looking for a technical solution but have you considered just yelling across the cabin at each other?

Of course #briar I knew I downloaded that for a reason.

I can report that our test of Briar worked perfectly.. (Except it was accidentally called Brian at some point.. ) I can see that sticking. - Our test was somewhat short circuited by #Ryanair's decision to actually seat us together in an #exitrow for once. #extralegroom baby!

Take the train instead!

There’s Meshtastic/LORA if you also like getting yelled at by airport security lol

I think Briar can do that

Write something in your notes app, screen shot it, send the picture. I do this with my OH on trains frequently.

Scuttlebutt?

Even though there are really good open source app but I'll not recommend this as Bluetooth itself is very very insecure