The claim of some people that the soul of somebody will be transferred to another person is baseless and it goes against the justice of God. Allah is fully able and He creates for every one his own body and his own soul. Allah's Justice will never put a burden on any one because of the acts of another person. Body and soul of every one will get the results of his faith and deeds and there is no point at all in a person having the soul of someone else. This false claim of incarnation came from non Muslims.
Those who claim incarnation need to prove it, and they could not and will never be able to prove their claim. It is just imagination with no evidence whatsoever.