Is it obligatory to pray twelve additional rak'ahs along with the two well-known rak'ahs of Istikharah for the prayer to be answered, and what is the ruling of Sharia on that?

The Istikhara prayer consists of only two rak'ahs, distinct from the obligatory prayers. The Prophet, peace and blessings be upon him, said: "If any of you is concerned about a matter, let him pray two rak'ahs other than the obligatory prayer, and then say: 'O Allah, I seek Your guidance...'" It has not been reported from the Prophet, peace and blessings be upon him, that he prayed twelve rak'ahs before it. It is best to limit oneself to what has been reported from him, peace and blessings be upon him.