You are a little confused about Ohms. resistance and impedance are BOTH measured in Ohms. A simple meter measures DC resistance. Totally useless for crossover design, as DC is zero Hz. Impedance varies with frequency. As said, you need the IMPEDANCE at crossover point.

Impedance ratings are an approximation, given by the manufacturer. DC resistance is usually lower, not uncommon for 8 Ohm speakers to be 5-6 ohms DC resistance.