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Yes, these are still fine to pick and consume. They will start to shrivel up after awhile, but even then they will still be able to be used, although not at appealing.

This article will give you more information about these: https://www.gardeningknowhow.com/edible/fruits/elderberry/tips-for-picking-elderberries.htm

As long as each stem has some roots, this can be done. Make sure to dig down at least a foot, until you don't feel tension from the root mass. This will mean that you have gone through it, and that it is ready to be dug up. Have them plant the new plants before it gets too warm to do so.

This article will have more information on growing these plants: https://www.gardeningknowhow.com/edible/fruits/elderberry/planting-elderberry.htm

Elderberries will fruit reliably with proper care. Usually, it is just missing something or is too dry to fruit. They do like plenty of water.

This article will help you care for these: https://www.gardeningknowhow.com/edible/fruits/elderberry/planting-elderberry.htm

This sounds and looks like Verticillium wilt, an often fatal fungal disease. Elderberry are among the group of plants that are susceptible. Unfortunately, this means you can not plant a susceptible species in that area. Here is more info including a list of most and least susceptible plants. http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/cankers/verticillium-wilt.aspx
Additional info: http://www.canr.msu.edu/ipm/uploads/files/woodylandscape_pdfs/verticilliumwilt.pdf

It, actually, looks more like symptoms of fungal infections. This is typical of overwatering. You can try a mix of wettable sulfur and dolomitic lime. This can help in most cases, but if it is too severe you may have to result to copper fungicides.

This article will give you more information on the care of elderberries: https://www.gardeningknowhow.com/edible/fruits/elderberry/planting-elderberry.htm