I have Carlsbro Alpha 400W 8ohm subs with passive crossover that feeds, via a speakon cable, to Alpha tops 250RMS also 8ohm.
I understand if I just chain speakers together (in parallel) I will get 4Ohm in this instance but is the total impedence in this setup with the crossover now 8ohm or 4 ohm. I assume still 8ohm somehow?
The resulting impedance of two 8 ohm speakers in parallel will be 4 ohm. Good efficiency crossovers have as high parallel impedance as possible, but you should check the impedance of your crossover model (by specifications or by measurement).
The bottom line is that in this setup you'll get less than 4 ohm total impedance, and I don't know how the amplifier reacts to that.