Some people from other schools of thoughts have raised questions and doubt the birth of Imam Mahdi(atjf) and they say cite thier reasons as:

1. There were 14 sects created after the death of the 11th Imam
2. His mother has different names, and the story of her being a Roman princess is a fabricated one
3. If he was divinely appointed then why was his birth a secret?

How would we respond to these outrageous claims?