We have a long vacation planned and paid for, but with elderly parents on both sides, we're feeling guilty. How can we handle this?

Husband and I have had a 5 week trip planned for long time. Husbands parents in 90's and live alone. We have been helping in their care with food/supply deliveries, etc. Husbands sister lives nearby and doesn't do a thing for them so they depend on us. My own father lives in a really nice assisted living home and was just placed on Hospice. I visit him weekly and my sister lives about 5 minutes from him - I live about 40 minutes away. Dad has heart problems, blind, and dementia, but knows us most of the time. My sister has an ocean home she and her husband go to on many weekends. Sister is making me feel terribly guilty for taking a much needed 5 week trip. Helping parents on both sides has taken a toll on me. Only God knows when any one of them will pass on. How do I handle my sister and her negative comments about our trip without feeling guilt? And if any of them passes while we are gone do we pack up and come home? Or stay put and enjoy our vacation the best we can? Don't want to appear selfish, but we are also getting older in 60's and need to have a life too.