No I mean 4 front calipers. 2 per wheel. That is how the car came. Stops pretty good.

By residual pressure valve is that a proportioning valve? If not how can I test this part?

Is the best way to check to see if the rod is holding is to jack up the car, push on the pedal hard and lock the brake and loosen the bolts on the master to the booster. If it releases it is the rod adjustment?

Yes it has a return spring and I have tried pulling up on the brake pedal when they lock up and it didn't help. The pedal was at the top of its travel.

It is only the front brakes. Rears are fine.

This is the first time I have ever seen both front brakes lock up. I have had sticking calipers on one side before but never this.

Thanks Again. I appreciate it.