You can do the following:
-let them skip pulls and don't let it bother you
-give friendly info about e-bikes
-he'll eventually have to move to a "greenway" ride at like 14mph
I don't see an e-bike as you age as a let down at all. Especially for a purely fun recreational group trying to keep folks together. It might be a conversation to have over a beer man to man or woman to woman or whatever. They'll likely admit to as much as they feel and then consider it. Just be positive and on point about wanting to keep them coming out and enjoying.
There's things an e-bike can let many riders see or do that wouldn't be fair otherwise.
When I took my bike to France for work, there were folks going up into the mountains on e-bikes with a big smile looking around that NEVER would have made it on a normal bike. Even with a 34/32. It made me happy seeing those people. And they weren't "gassing it" like a moto either. Just a normal climbing pace of a normal manual bike.
I've changed my mind a lot on e-bikes and think they have a very good place in the world for quite a few people.