Since you describe the hoses as new, they are unlikely to be the problem. The same is true of the front calipers. What kind of shape are the rears (hoses and calipers) in? I suspect the problem is most likely a weak master cylinder. Another possibility is that if the car sat for a while (a few days or longer) with the brake system apart, all the fluid would have drained completely away, and it might be necessary to bench-bleed the master cylinder to purge it of air before it can pump fluid effectively. (though I would have thought that pressure bleeding would have eliminated this problem)

There is a certain specific order for bleeding---I've always been careful to follow it and never had problems.

A friend once had a 142E on which the rear calipers had been installed on the wrong sides (left caliper on the right side and vice versa) and because the bleeder screws were then at the bottom of the caliper, it was impossible to get all the air out, or get anything more than mush at the pedal.

When bleeding, the switch for the brake failure warning light should be removed from the junction block, otherwise it can be damaged and the light will come on when there is nothing wrong with the brakes (it happened to me many years ago on a 72 145)

The thing with Fiats (124s, and possibly others) was that the rear brake proportioning valve was connected to the rear axle by a linkage rod, so that when the car nosed down under hard braking, pressure to the rear calipers was reduced to keep them from locking up. When the rear wheels were raised off the ground, the valve would completely block pressure to the rear, making it impossible to bleed. It is necessary to put the jackstands under the rear axle in order to bleed properly. The proportioning valves on a 140 (there are two of them, due to having each rear wheel on a separate circuit) work on a different principle, and it shouldn't matter if the axle is supported or not.