Well to be perfectly honest, my DH had no problem telling his Mom that half of her $150 credit belonged to us. I also have no doubt that my 2 DSs will hit her up for far more than $150 on the cruise. She is quite the generous grandmother.
It's really just the principle of the situation that makes me mad. What even mad me angrier was after I read my post, I remembered that we may have used points for myself and DH but we paid cash for the two kids. Couldn't they give us a $75 shipboard credit? Oh well, life goes on.
I'll still have a great time on the cruise. And, I still love DVC.