Perhaps the large one is Contracted datana - although I have been unable to find what it looks like in its adult phase.

or is it Symmerista albifrons.

Yep, I got 'em too. Actually I get them every year. If you blow on them, they usually arch back in unison into a 'C' shape.

No need to worry, they won't harm the plant and they might provide a little food for a hungry bird.

I also have them now on one of my Fothergillas.

I also get them every year and look forward to seeing them, but I cannot figure out what butterfly they turn into. I guess they get eaten before they can change. I had one left yesterday evening and it is gone this morning. :(

I don't think that most caterpillars transform on the bush on which they feed. Once they are done eating (and growing), they walk off to find a place to turn into a butterfly (or moth). One year I had some milkweed in pots and there were other potted plants nearby. I always found the chrysalis hanging on a different plant, never on the milkweed.

Here is a link that might be useful: A bit of an explanation about the process