really, if we wanted to pick and choose, we would have also included bibi zainab, umm kulthum, bibi khadija, hazrat abu talib, hazrat abbas, the lot, theres no shortages. But that not how the system works, you either obey the Prophet (saw) and the Imams, or you undermine them and choose your own.
Theres plenty of ahadith that indicate clearly who the Ahlul bayt were. When ayah tatheer was revealed, when mubahila took place, and the simple act of the Prophet (saw) of going pass Imam Ali (as) and bibi Fatimas door, every morning at fajr, and reading the ayah tatheer loudly....for about 6 months after the ayah was revealed. Why do folks tend to ignore and undermine the prophet (saw) when it goes against their wishes? Is that really your idea of submission?