Why are my blind dogs suddenly tired, not eating, and collapsing?

I recommend to have both your dogs examined by the veterinarian. Just like humans, many diseases can have the same clinical signs and so it is impossible to know the cause without a physical exam and likely some diagnostics. Being unbalanced and collapsing is extremely concerning for an issue with the heart, blood pressure or the brain. Other conditions can also cause collapse. Fatigue can be seen with many conditions as well and it could range from internal parasites to an autoimmune condition. Have both pets seen within the next day. Diseases tend to have the best outcome if they are dressed early. I hope this helps.