I wonder...I think the OP is asking if the cards will work in the FP scanner without being checked in at the gate. I don't know...has anybody tried this?
Also, you probably would get a return time on the FP which is too early for your family to make, since you'd have to return the cards to them in order for them to get through the front gate.
If your family is only going to be an hour or so behind you, and you run to the park, admit yourself, take the cards to the FP machine, collect the 5 FP's, hop on a ride or 2 (you have an hour to kill, right?), then run to the front gate, exit, meet your family, return their cards, all get re-admitted, and make it to the ride w/in the return window...hey, it might work fine!