Probably dead/dying, but don't toss them until next summer when you know for sure they're dead. I had a spruce my son dug up in July last year lose every needle only to bud out very hard this spring.
You should be able to find more white pine very easily this fall or next spring in the same location. It's a climax tree and from my experience if you find some seedlings in a forest you will absolutely find many, many more if you look.
For more hemlock, be on the lookout for the big, old trees. In my experience the seedlings stay relatively close to the big trees, and can be in slightly isolated pockets. Near me, hemlock often grows in beech/maple forest, so if you're struggling to find more hemlock, try searching for beech/maple communities, which are much easier to find than hemlock itself.