Jessica first let me say I am so sorry for your loss. My father passed away this past New Years Eve (6 months before our wedding) I was devastated. I am still grieving although it has gotten a little easier. The first month it was hard for me to even get out of bed and I would cry all the time. I never thought about canceling the wedding. My father loved FI and I know he would not want us to cancel or postpone the wedding. It will def be hard for me with him not being there to walk me down the aisle or to dance with but I know he will still be with us.
I would give FI a little time before you bring up anything about canceling the wedding or not...he probably isn't thinking very clear at all right now...but I bet your FFIL would prob not want you to cancel and it is def good for the family to have something positive to look forward to. You would be amazed by the human spirit and how much it can actually endure and still go on! If you need to talk please don't hesitate to PM me.