When replacing the front U-joints with greasable Joints, do you normally replace the 2 on the shaft or all three on the front? and do the knuckles tend to were out and you have to replace those as well?

Thanks,

 

While I had mine out I had them replace all of them, just to be safe.

 

What knuckles are you refering to?
By your post, I would think you may not have the mechanical savey to tackle rebuilding a double cardon.
And yes replace them all if you have not had them greased every 12,000 miles. Also grease both slip joints on both drive shafts as well as inspect the roto flex for cracking and possible replacement.