Your appeal to the Sahabi Zayd concerning the understanding of this tradition does not hold water. In Saheeh Muslim, and we know for certain he narrated it during very old age when he complained of memory problems, he is adamant that the Ahlulbayt do not include the wives. If your scholars themselves claim that it is common knowledge the Ahlulbayt include the wives, you can not have your cake and eat it, so to speak dear brother.
No one is challenging the understanding of Zayd bin Arqam(RA) it is unchallenged and spotless, for the obvious reason that he witnessed the event when Prophet(S) said those words. I'll give a chance to someone saying he missed some wordings while narrating it due to old age, but no way one could say that he misunderstood that Ahl al-bayt are all those members of household whom upon acceptance of was forbidden. That would be a preposterous claim, because even old age wouldn't make him form that view.
But yes, he was mistaken in it's application(NOT UNDERSTANDING) because he wasn't aware of the special status of wives of Prophet(S) in regards to not receiving Sadaqa(charity), which was contrary to wives of common Muslims. Yet, Zayd(RA) did consider wives to part of Ahl al-bayt in general, which implies that they are still part of Ahl al-bayt mentioned in Tatheer, since Thaqalayn and Tatheer have no relation. Because your own reports doesn't count Fatima(RA) in Thaqalayn. So, even if you want to go with Zayd's(R) view that wives of Prophet(S) weren't eligible to receive Charity, as some Sunni fuqaha do hold, then that's not an issue, because it still disapproves your misinterpretation of Hadeeth Thaqalayn which is contrary to the understanding of an eye-witness Sahabi.