Unfortunately, I have had too much experience with cancer so I truly sympathize with you and your family!!! I lost my mom 6 1/2 years ago & recently helped my mother-in-law through her bout, not to mention plenty of other close friends and family before my mom. There is no real right way or wrong way to deal...you have to feel the way you feel - especially with the shock being so recent. Crying is OK right now, but remember, there has been nothing definitive & so things could be better than you think. The diagnosis isn't necessarily a death sentence. As time goes on, the best thing to do is stay informed about everything that is going on & remain as positive as possible no matter what. Despair will only bring defeat. Now is the time for your family to really rely on & support each other. If you &/or your sisters live in the same town as your mom, help her by going to dr. appointments and such with her. I was at college when my mom went through her bout & missed a lot of things, partly because I didn't want to admit that there was anything wrong. I think that hurt her a lot in the long run. However, I was by my mother-in-law's side as much as she needed me. Don't be afraid to show your emotion whether it is with your family or a close friend & don't be afraid to seek counseling either.
I am praying for you & your family