Jeremy-very very sorry to hear the news. Went through similar with my Dad 10 years ago this Nov. Tell your Dad you love him, tell him you're proud of him. Tell him not to worry about your mom, the family will take care of her.
Just hang in there, be strong for your family, and hope for the best possible outcome (quiet, peaceful, painfree, surrounded by family). Each family/situation is different, but it helped for us by being able to have Dad at home, in familiar surroundings.
Sorry, Formo, I'd type more but this is hard.