low pass crossover

I pararell my 2 x 4 ohm speaker, it would be 2 ohm load.

My question is, If I want to apply the passive crossover in my speaker,... which chart should I use 4 ohm or 2 ohm?

And what should I use, narrow band pass or band pass crossover for mid range(not mid bass) speaker?

If you plan to run 2 mids in parallel, build your passive crossover for the 2 ohm load.  That way you only need to build one circuit.  Use the "bandpass" formulas for a typical midrange speaker.  The high pass section (low frequency filter) is generally more critical than the low pass section in terms of "getting it right" for the particular drivers you plan to use.

The disadvantage, of course, to using passive crossovers instead of using an active filter on the low level side is passive circuits are very difficult to adjust, as you must physically remove and replace components if the sound is not right the first time...

Good luck.