Please don't panic. All of your birds are not going to die. If you have red stars, a production breed, they usually do not live nearly as long as heritage breeds. Delawares are heritage breeds so they should be around for a while for you. I have no idea about your blacks since I do not know their breed. I would ask your neighbor what breeds your birds are. If you got them from him/her, they might not be production birds. Maybe your hen is just ill. I would put some vitamins/electros in their water & see if she improves.
Production breeds die very young , usually at 1 1/2 to 2 years old. They are typically sold at feed stores, hatcheries and TSC/F&F type stores. Usually they will be listed as "production" or "sex linked" birds so you know what to be aware of.
Your average heritage breed, given good lineage & care, should live a good 5-8 years or more. They do not lay as often as production birds and will gradually slow down as they age in how often they lay an egg, but they will give you many years of enjoyment. HTH