I'm planning a birthday party for my sons 8th Birthday with games/prizes but only one kid's mom responded-help

I have no idea how many kids are coming cause the parents never rsvp-ed me back and I can't call them cause of privacy rules at the school. We aren't sure if the kids ever brought the invitation home! My husband has enlisted his sister and mother to make stuff for the party such as food--which I was totally against in the beginning and now they are getting involved with why only one kid is showing up and not the 12 we invited.not to mention they view this to be the Biggest Birthday EVER for a youngster I have oher views on that--which proves this shouldn't be made out to be the biggest ever since only one kid has responded in the week I allowed for responses. My son now faces the disappointment of a good party gone bad because all but one are coming. Any suggestions??