How do I tell them their dad has cancer?

D • Mama of 2,lost an angel, waiting on number 4💘💓💘 married-blessed💓
So we have a very smart 5 year old baby boy. My husband got diagnosed with stomach cancer a 2 days ago and obviously our 5 year old noticed something is going hella wrong because I'm constantly crying and freaking out and my best friends are watching him and our 7 month old basically all day long. They came to the hospital room twice now and when he asked whats wrong my husband laughed it off and said "I ate too much candy now I'm sick" but I think we'll need to tell him because honestly if this wont end good he needs to understand that. Does anyone have any advice how to tell him? And our boy we're going to adopt who's in Germany and 4 years old, still waiting for us to come over. How am I going to tell this the kids?
I dont think this is the right group but I dont know who to ask none of my friends have children or are pregnant and I didnt tell my parents yet because they're on their way to the States and my husband doesnt want them to be scared.
His dad is dead and we havent seen his mom for months now.