Since the rotors are so far gone just start over. I would get pads too even though yours have some life. You never know when the old pads will fail. And they don't cost that much in a kit.
Also verify that everything is working while doing the parts.
Check that the pads can move against their brackets. They always stick.
Your rotors have so much corrosion that there's a possibility the pads aren't hitting them if the calipers are at all siezed.
They can seize at the slides or at the the hydraulic pistons or both.
Remove corrosion, clean and lubricate any slides.
If you have a hydraulic surge system you can usually look up how to pump the master cylinder at the tongue.
On mine I was able to have my helper pump my brakes with a lever in the top of the coupler.
If your hydraulics haven't been serviced in the last few years it's a good move.
You may even want to do a bleed, wise thing.
