Update,last night I rented a Disc Brake Caliper Service Kit.

With that I managed to get the left rear together, but I had to give up on the right rear.
I think perhaps the caliper is frozen/bound and the piston just wont retract anymore. I also noticed the lever holding the e-brake cable is not in the same position as the other side. I tried to free it but had no luck.

I'll have to figure out how to adjust it some other day.
So that left side has one old and one new pad for the time being. Once the other side pads develope some wear, I'll relocate them to this trouble side. Braking seems fine even with this half assed configuration.
Thanks for the advise above!