Have you tried dead heading all the hydraulics?

 

In other words, cycling everything until it bottoms out several times? You're supposed to hold the hydraulic pressure for a few seconds, then cycle the other direction, providing you have a loader.

 

generally, only single acting cylinders might need to be bled.

Even cylinders that have more hose volume than cylinder volume will bleed themselves (dead heading as mentioned above)

Single acting bottom port vertical cylinders are the primary exception. You will often see cylinders like this on dump trucks. They usually will have a bleeder installed at the top.
ps. don't open the bleeder and then send flow to bleed them either. lift the body up a bit, then crack it slowly is how I recommend to do it. much less likely to spray oil everywhere. I've seen some real messes.