I am sorry to read this, LQ.
Your sister can’t have been any age? I hope you and your dad are ok.
Queenie, my most sincere condolences on your loss… 
Both my parents died a couple of decades ago and my brother and I are still this side of the grass. My brother however has lost his youngest son to cancer when still in his 30s (the son that is) which did upset my brother greatly.
I don’t know how I will feel if my brother were to die, growing up we weren’t particularly close but have become more so since our fifties despite living on opposite sides of the planet, fortunately I am the eldest so hopefully it is not an emotion I will have to deal with.
Really I cannot add anything to what has already been said, it must be awful to lose both siblings.
Bev I’m so sorry to hear your sad news x
You’re bound to have mixed emotions but let yourself grieve for your sister.
Look after yourself and your dear Dad
(((Hugs)))