I'd suggest that you take the pads out of the calipers and mount the calipers and work to get them to slide on the pins---
push the pistons into the calipers with a c-clamp and reinstall pads and back on car--with the brake lines off you can use a little compressed air to apply the brake and release, do it again and again til you get it free and easy then hook up lines, bleed,etc.