Lots and lots of small and medium trees would work. Almost too many to list!

What about something like birch? It's deciduous, but in zone 6 who sits out in wintertime, so concentrate on spring/summer/fall privacy.

I think you've got the right idea with the trellises. You could do both trees and trellises or think about building a structure that blocks their view entirely and provides you a little sanctuary in your yard.

Thanks for the ideas!! Building an arbor like that would be great actually and it’s something I hadn’t thought of. That second picture you posted is actually really nice!

Since I imagine that you largely want privacy in warmer weather rather than in winter, look at medium sized deciduous trees. A few of my favorites are redbud, flowering crabs, hornbeam/musclewood, basswood/Tilia americana.

The idea of structures such as thr trellises or arbor with vines that tolerate part shadewill help as well, so perhaps you can mix the two.