I can almost guarantee this will not work out. Different guitarist, different tone. If I were you, I would either record the pieces mistakes and all and either leave it or have him redo when he feels well enough. If the fellow is very ill and old, take what you can and consider it a documentation rather than just a recording project. In fact I would include some of the dialogue in between as well.

Classical and flamenco do not take well to overdubs. I can tell you that from experience. Mood changes, seating changes, fingers get tired, people get tired, humidity. So many factors. If he can just play through with the mistakes and all, be happy and enjoy it. You are capturing a moment that will never be lived again.

Every guitar and every guitarists rig sound different from each other. Difference in technique and playing style also. So it will be nearly impossible to have other folks match his stuff. All you really need to do is get enough takes from this guy to composite together in one complete good cut. That's how many folks are recorded to date overall. Multiple takes to create a flawless composite take. We don't necessarily do punch ins anymore like we did in the old analog days. Even then, I was taking full takes from the multiple takes to create a composite of a single good take.

Your interest is composited daily.
Mx. Remy Ann David

Thanks, I been triying to do multiple takes as well, but the difficult parts are always bad. The documentation point of wiew could work as a last option

What about if is a different musician but using the same guitar , the instrument I mean

If you're using the same instrument through the same amplifier, in the same room, you might get by. But there will always be that noticeable difference in playing style and technique. I mean, you could daily wear your girlfriend/wife's underwear and most people wouldn't know. But there will be those that will. You don't want those panty lines. And you also don't want anybody to see those industrial latches on your brassiere. Though maybe you do? It's all in your style and technique and their technique also. Two different people with the same car will drive them differently. But if it's your only way, you've got your work cut out for you.

You shall prevail
Mx. Remy Ann David

If you bring in another guitarist, might as well have him do the whole thing, for continuity.
Hopefully you have sheet music for him to study.

For me no matter what guitar I play it sounds like me, the tone, and nuance comes from the hands.

:cool:

And that difference is exactly what everybody is talking about. He is always going to sound like him and somebody else isn't.

Thankfully I sound like me
Mx. Remy Ann David, me