Must prayers in which an obsessive person unintentionally interjects words be repeated, knowing that the words may exceed two letters and may be audible?

You must ignore the whispers (waswas) and pay no attention to them. If you spoke during prayer under the influence of waswas, unintentionally, then that does not invalidate your prayer and does not harm you, because you are in the position of someone compelled. Allah has forgiven this Ummah for mistakes, forgetfulness, and what they are compelled to do. We advise you to consult doctors and the counseling section of the website.