Well, really, those are just trunks right now, mostly straight with no taper. Most of the tree would not be of any use, though you could try air layering if there is anything that looks interesting in the canopy. Otherwise you'd probably have to chop them pretty low and grow the next trunk segment...and then do that again. Multi-year project.
As for the rest...what kind of roots are there? If those are lousy (and they usually are unless you prepared the trees when planting, and dug them periodically to work on the roots...which wasn't done here) then you'd have to do a ground layer most likely to fix that. That adds in another year or more for the layer to take, then years for the roots to develop.
So I think these would be long term projects at best...many years to produce something of use. You might be better off getting more seeds or seedlings and start those properly - set the roots, plant in the ground, then dig periodically and develop them from the start. Might be as fast or faster than trying to use these.
That said, you can certainly experiment with one of these, learn how to develop the next trunk segment, learn how the tree responds to pruning, root work, etc.