As nobody else is replying here is a Pilots who operates that type of props shall we say ideas.
The props will be on what's called the start locks which get selected by selecting reverse while the engine is winding down and the oil pressure is dropping. So they engage in a ring as they relax back towards the shaft as the rpm comes down. They are held out the way by centripetal force when the engine is up to speed.
I wouldn't say you have an armed and dangerous prop sitting there which is likely to suddenly go bang. We have had a prop that's been stuck on the locks and it was sent to the prop shop in that condition and it eventually came back. How they dealt with it I don't know but I suspect there will be an stupidly big jig which is able to hold the front casing under pressure as the retaining bolts are removed and then gradually eased off to release the spring.
The main thing to note is not to muck about with the bolts in the hub. I really don't think you can do it on site as we "had" to send it back to the prop shop they couldn't do anything with a site visit.
To get them off in the field you not only would have to provide oil pressure but you would also have to have it spinning. And if its been sitting there for years there is a reasonable chance they won't come out anyway.