I have to agree with the others; getting married when you're just now dating wouldn't be a good idea. It's really, REALLY sucky that her dad is passing away...but that just is NOT the solution.
As for your friends and all...well, that's a tough one. I personally feel that the sooner you come clean with everyone, the better. Yeah, they'll be angry that you lied to them. You may have to part ways with them for a while before they are ready to forgive you. But really, owning your relationship right now and being open and honest about it is more important than sparing a few people's feelings.
Like others have said, if they are truly your friends, they'll be okay with it, even if it takes them time.
