33:30 - O Consorts of the Prophet! If any of you were guilty of evident unseemly conduct, the Punishment would be doubled to her, and that is easy for God.
33:31 - But any of you that is devout in the service of God and His Apostle, and works righteousness,- to her shall We grant her reward twice: and We have prepared for her a generous Sustenance.
33:32 - O Consorts of the Prophet! Ye are not like any of the (other) women: if ye do fear (God), be not too complacent of speech, lest one in whose heart is a disease should be moved with desire: but speak ye a speech (that is) just.
33:33 - And stay quietly in your houses, and make not a dazzling display, like that of the former Times of Ignorance; and establish regular Prayer, and give regular Charity; and obey God and His Apostle. And God only wishes to remove all abomination from you, ye members of the Family, and to make you pure and spotless.
Verse 30-32 says the wives of Prophet Mohamed (S) are susceptible to sins and therefore precaution is warned to them as their punishment is double than common women.
Refer the bold text above - Allah is making Ahlul Bayt as pure and spotless. As they are spotless & pure hence they are NOT susceptible to sins, but Prophet wives are indeed susceptible to sins & double punishment. Hence as per Quran wives of Prophet are not part of Ahlul Bayt.
Hadith below are in line with Quran verses above:
Narrated Yazid Ibn Hayyan:
We went to Zaid Ibn Arqam and said to him: You have found goodness (for you had the honor) to live in the company of the Prophet (S) and offered prayer behind him, and the rest of the Hadith is the same (as 3 traditions before) but the Prophet said: "Behold, for I am leaving amongst you two weighty things, one of them is the Book of Allah...", and in this (Hadith) these words are also found: We said: "Who are his Ahlul-Bayt (that the Prophet was referring to)? Are they his wives?”
Thereupon Zaid said: "No, by Allah! A woman lives with a man (as his wife) for a while; he then divorces her and she goes back to her parents and her people. The Ahlul-Bayt of the Prophet are his lineage and his descendants (those who come from his blood) for whom the acceptance of charity (Sadaqah) is prohibited."
Reference:
• Sahih Muslim, Chapter of virtues of companions, section of the virtues of ‘Ali, 1980 Edition Pub. in Saudi Arabia, Arabic version, v4, p1874, Tradition #37
Zaid Ibn Arqam said: I have grown old and have forgotten some of the things which I remembered in connection with Allah’s Messenger (may peace be upon him). So accept whatever I narrate to you, and which I do not narrate do not compel me to do that. He then said: One day, Allah’s Messenger (may peace be upon him) stood up to deliver sermon at a watering place known as Khum (Ghadir Khum) which is situated between Mecca and Medina.
He praised Allah, Extolled Him and delivered the sermon and exhorted (us) and said: "Now to our purpose, O people, I am a human being. I am about to receive a messenger (the angel of death) from my Lord and I shall answer that call (would bid good-bye to you). But I am leaving among you two weighty things: the one being the Book of Allah... The second are the members of my household (Ahlul-Bayt). By Allah I remind you (of your duties) to the Members of my House (saying three times)."
He (Husayn Ibn Sabra) said to Zaid: Who are the members of his household? Aren’t his wives the members of his family? Thereupon Zaid said: His wives are among Ahlul-Bayt but here Ahlul-Bayt are those for whom acceptance of Zakat is forbidden. And he said: Who are they? Thereupon he said: ‘Ali and the offspring of ‘Ali; Aqil and the offspring of Aqil, and the offspring of Ja’far and the offspring of Abbas.
Reference:
• Sahih Muslim, Chapter of the virtues of companions, section of the virtues of ‘Ali, 1980 Edition Pub. in Saudi Arabia, Arabic version, v4, p1873, Tradition #36.