Did you pump up the brake pedal and pump the handbrake up after fitting them? Also as you have only changed the pads, and not also the disc's, the new pads don't have full contact on the disc until the pads bed into the disc's. Old disc will always have groves, and wear, until the pads bed in the brakes will have a soft feel to them.
brakes can tend to be soft after replacing them
if they work just try after a day or 2 see if they get better
why did you change the rear callipers
maybe a issue elsewhere does the civic have a compensator valve
If you've changed the rear calipers you must do a full bleed. All corners need bleeding. I use a pump and suck the fluid from each bleed nipple, saves having someone pumping and closing and opening the bleed valve, however I have someone watching the brake fluid resevoir.