The standard water lines are hard lines, I cant remember if the turbo feed is a hardline or not, but it could be that with the heat over time they have moved and are pressing against the banjo trying to push it one way when the banjo bolt wont move obviously because its screwed in. If this sounds like whats happening then I would continue to undo the banjo bolts
Seeing as it sounds like you have an aftermarket turbo this might not be the case. there should definently be no pressure in the oil feed or drain, as any pressure bleeds off pretty much as soon as the engine turns off. The coolant lines will have coolant in them of course, but when cold it should just be coolant at ambient pressure, pull the radiator cap off and it should bleed off any pressure thats in there (Be careful it doesnt spew out at you, but this shouldnt be a problem unless the car was hot)
Let us know how you go. Good to see your not just giving up because someone before you didnt know what they were doing