Brake emergency

Alright, just spent 2 days with my elderly father-in-law, he was a brake installer for 30 years, years ago. He was excited to help me replace all the brakes in my 1966 dart, 270, 225, L6. 9in brakes.

I gathered up all the parts, we ended up not completely replacing everything.

Front wheels got repacked, new bearings, new seal etc... one front wheel got a new cylinder. all new shoes, new adjusting sets (try tracking those down). The one front wheel that got a new cylinder, also got bled. No other wheels got bled.
Front brakes work great.

Rear: all new shoes etc..., cylinders appeared ok so kept them. One rotor was bad, but the other was good.
Installed and adjusted. Engaging the EBrake seemed to cause issue, wouldnt release etc... I worked on the cable, let it out a little, cleaned up the grungy mount parts. Seems to slide in/out better.
The driver side rear wheel is screwy. Parking brake is off. I start the car, put foot on brake, shift into D and I feel the pedal release a little. Let foot off brake and Left rear wheel begins to spin, then I brake normally, wheel comes to a stop, but then I release brake and the wheel remains stopped, I press brake, wheel spins, release brake wheel stops. The Right rear works as normal, although doesnt really come to a complete stop, But I think that just needs some adjusting.

Curiously, I removed tire and drum on the driver rear, and (engine off) slowly apply brake and the cylinder is very slow to react, and when it does it is the Left piston. The right one doesnt really move, until after a few times.

So now I either think the wheel cylinder is bad , or there is a bunch of air in the system that is displacing the fluid, causing the other tires to pull all of the fluid leaving none for the driver rear? Does that make any sense?

Help and any thoughts?