Aubree,
Sometimes just being the one who does NOT have all the background and knowledge is the best thing. You will be able to offer Dad so much in the way of encouragement and support of a completely different kind than your siblings. With each of you able to offer him and your Mom so many different types of support and HOPE, it will make this journey much more bearable.
Please also read some of the survivor stories and good news postings. There are so many wondeful people here who are surviving and thriving. There is no reason to think that Dad will not be one of them.
As overwhelming and upsetting as this is right now, it will get easier to cope once the treatment begins and things get into a routine. For now, just let your Dad know you are there for him, cheer him on and remember, there is HOPE..
Keep us posted
Sending lots of hugs and positive thoughts to you
Christine