All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Ibn Hajar mentioned in his book Al-Isaabah quoting some scholars that Umaamah bint Abi Al-‘Aas neither had children from ‘Ali nor from Al-Mugheerah ibn Nawfal ibn Al-Haarith ibn ‘Abdul Muttalib who married her after the death of ‘Ali . However, he (Ibn Hajar ) quoted some other scholars as saying that she had a son from Al-Mugheerah who named him Yahya and he used to be nicknamed by him (i.e. he used to be called Abu Yahya).
As regards the details on what is meant by Ahlul Bayt (i.e. the family of the Prophet ), please refer to Fatwa 87526.
Allaah Knows best.