It was bled by compressing the brakes, with clear tubing run into a bottle of fresh fluid. Large amounts did seem to move every time they were pressed.
He pretty much said he was certain that it never was the caliper, and my brother replaced it for no real reason, so the back right one isn't getting replaced. He told me it was the hydraulic system, probably the master cylinder specifically. I forget what test he did to check the brake lines, but he said they were fine. I suppose we'll find out tonight after the new master cylinder is in.
I was just bewildered why the front left would seize.... a new caliper is put in, and then the back right does, and the front left seems fine.