Scholars differ on sending blessings upon the Prophet in Tashahhud. Opinions range from it being a pillar, obligatory, or Sunnah. Most likely, it is Sunnah, not invalidating prayer if omitted.

It is not permissible for a non-Muslim to pray either in the ranks or on his own. What he has to do is to enter Islam before he prays, then to purify himself by doing ghusl and then fulfil the conditions of prayer.