You do not want to run 4 speakers off of one passive crossover.
Passive's xover frequency and other things are designed specifically for a certain impedance. If you change the impedance at the passive, you will change the crossover frequency and potentially cause other features of the crossover to not function as intended.
You need to use all of the crossovers the speakers came with.
but you can connect the input wires together so you only have one set of wires to run from your amp, and you will be running at 2 ohms on your amp which will give you more power
More but probably not double. Each set will be getting less power than a single set would running on 4 ohms. Don't get me started on the freq response ramifications of running a second set of speakers up front...