Do a compression test on all 4 pots and look at the plugs while they are out. If oil getting into cylinder chamber they will be oily.

That would give you and starting point to find out where the oil is going.

If thats OK, I would be looking at the oil feed to the turbo and drop off the outlet hose and see if the turbo is full of oil. May tell you if the oil seals in the turbo are shot.

???? Im no guru either but a bit more info may help others get a better idea of whats going on.