The ayat , which Pagluu mentioned concering two of the Prophets PBUH wives, needs to be looked at in its context.
The actual Surah mentions that the Prophet PBUH confided a certain matter to one of his wives, who contrary to his instruction disclosed it to another. Both the wives were warned by Allah to seek His repentence, which they actually did, for what they had done. Allah also warned ALL the Prophets wives that they could be divorced and replaced by others and that they they were in no position to do harm to the Prophet PBUH. All the wives actually took this warning on board and actually abided with the warning.
This ayat does NOT mean that Hazrat Ai'Shaa RA was predicted for the future as the notion by some people implies and is in the same league as Hazrat Nuah AS and Hazrat Lutt AS wives.
Furthermore, did the Qur'aan make a mistake in stating that the Wives of the Prophet PBUH are the Mothers of all the Believers? and should only be contacted via a Screen?
This instruction applied to all the Believers and is very clear.
Secondly, the wives of Hazrat Nuah AS and Hazrat Lutt AS were actually mentioned in the Qur'aan and their characters are also described including their punishments:
066.010 Allah sets forth, for an example to the Unbelievers, the wife of Noah and the wife of Lut: they were (respectively) under two of our righteous servants, but they were false to their (husbands), and they profited nothing before Allah on their account, but were told: "Enter ye the Fire along with (others) that enter!"
If the same was of the Wives of the Prophet PBUH, then the Qur'aan would of mentioned this in clear terminology.
Thirdly, the Ahl'Bayt does NOT apply to only 5 members of the Prophet PBUH household. This is made very clear in the Qur'aan. When the families of the Messengers are mentioned it includes all members:
003.033 Allah did choose Adam and Noah, the family of Abraham, and the family of
‘Imran above all people,-
028.029 Now when Moses had fulfilled the term, and was travelling with his family, he perceived a fire in the direction of Mount Tur. He said to his family: "Tarry ye; I perceive a fire; I hope to bring you from there some information, or a burning firebrand, that ye may warm yourselves."
033.032 O Consorts of the Prophet! Ye are not like any of the (other) women: if ye do fear (Allah), 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.
033.033 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 Allah and His Apostle.
And Allah only wishes to remove all abomination from you, ye members of the Family, and to make you pure and spotless.
Please take note, that the above ayat is specifically related to the instructions to the Wives and then mentions the Family.
Therefore, the Qur'aan confirms who the Ahl'Bayt is, without a shadow of a doubt. It includes ALL the wives.
Finally, the question still remains, did Hazrat Ali RA keep in line with the Qur'aanic ayat concerning the Wives as Mothers and dealing them via a screen.