What is the ruling on reciting the Tashahhud and the Salawat upon the Prophet (peace be upon him) aloud during prayer for someone with obsessive doubts (waswas), and does that invalidate it?

Reciting the Tashahhud (definition) aloud and sending blessings upon the Prophet (peace be upon him) is disliked, but it does not invalidate the prayer. Sending blessings upon the Prophet (peace be upon him) to remove the whispering (waswasa) regarding the pronunciation of letters. The whispering concerning the articulation points of letters is from the stratagems of Satan, so one should strive against oneself to abandon it, seek refuge in Allah from the accursed Satan, and turn away from these whisperings.