No.

Josefumi and YoJo became one on a biological level.

Gappy's DNA is both of them, and he is them.

Its the same reason why Josuke couldn't revert Nijimura Sr. Back to normal.

Understandable

No bc half of josufumi and Kira are dead

Kinda

I think that it's a pretty interesting theory

He can take away his 4 testicles

No, he can’t bring back people from the dead, or bring back their memories, also it be really boring if a simple ability like cd’s healing would reverse an action done by the walls eyes which is implied to be powered/made holy by either the corpse of Christ or johnnys corpse.

No

Well actually

It depends

Do you think Jsefumi and Kira are dead?

If so then yea no...

But if you think they are still inside Gappy, then yea CD can 100% do it.