You can’t measure impedance with an ohmmeter. Although impedance(Z) and resistance(R) are both quantified in ohms and aren’t completely unrelated, impedance applies to AC signals. It’s not going to be the same as DC resistance. It’s going to depend on frequency and is measured at 400Hz. You can buy a meter which reads impedance, but it’s unlikely an ordinary VOM will be able to do it. But you can reliably say that the effect of two impedances in series will be additive. In parallel it’s more complicated, depending on how many speakers and what the impedances are: 1/(1/Z1+1/Z2+1/Z3…), so four ohms for two 8 ohm speakers in parallel.
I would expect that if the amplifier is designed to drive two speaker chains, then each chain would have about the same combined impedance. This should be verified by the manufacturer’s documentation. If you end up with a low impedance speaker chain, it will place a higher load on the amplifier, which may or may not have consequences.