^Meray bhai, main point is that Bibi Sarah was Ahlul Bayt of Ibrahim (as) because Allah (swt) considered her deeds high enough to be part of the chosen members of the household (ahlul Bayt). Being a blood relation (like in Nuh's case) let alone being a wife (like in Lut's case) is not enough for one to earn the lofty status such as the one Allah (swt) granting to the chosen people in the Quran such as:
3:33-34. Allah did choose Adam and Noah, the family of Abraham, and the family of 'Imran above all people,- Offspring, one of the other: And Allah heareth and knoweth all things
4:54 Or do they envy mankind for what Allah hath given them of his bounty? but We had already given the people of Abraham the Book and Wisdom, and conferred upon them a great kingdom.
As for the importance of Ahlul Bayt, you are free to choose any alternative to them but here is why its important to know them:
{Al Quran 25:57} قُلْ مَا أَسْأَلُكُمْ عَلَيْهِ مِنْ أَجْرٍ إِلَّا مَن شَاء أَن يَتَّخِذَ إِلَى رَبِّهِ سَبِيلًا
Say: "No reward do I ask of you for it but this: that each one who will may take a (straight) Path to his Lord."
{Al Quran 42:23} قُل لَّا أَسْأَلُكُمْ عَلَيْهِ أَجْرًا إِلَّا الْمَوَدَّةَ فِي الْقُرْبَى وَمَن يَقْتَرِفْ حَسَنَةً نَّزِدْ لَهُ فِيهَا حُسْنًا إِنَّ اللَّهَ غَفُورٌ شَكُورٌ.....
...Say: I do not ask of you any reward for it but love for my near relatives; and whoever earns good, We give him more of good therein; surely Allah is Forgiving, Grateful.
{Hadith Thaqalain}
Sahih Muslim, Vol. 2, 238; Musnad Ahmad ibn Hanbal, Vol. 5, 181-182; Sahih Tirmidhi, Vol. 2, 220.
The Messenger of Alláh - may Alláh bestow peace and benedictions upon him and his Progeny - said: "Verily, I am leaving behind two precious things (thaqalayn) among you: the Book of God and my kindred (`itrah), my household (Ahl al*Bayt), for indeed, the two will never separate until they come back to me by the Pond (of al*Kawthar on the Judgement's Day)."
Well if teh above Hadith is correct then plz explain to me, we do have Quran now but why we do not have any Ahle-Bait for last 1400 years according to definition of Ahle-Bait that you have put forward.