Are material heretics members of the Church? Tell us why Van Noort and company are wrong...
While there's some dispute over treams (as some theologians hold that due to the etymology of the term, those in material error only should not be called "heretics" at all), absolutely material "heretics" are members of the Church.
You're the one who's wrong because you don't understand the terms, conflating manifest heresy with material heresy ... and additional confusion in the terms was added by those who tried to re-define "material" heresy as referring to those who are are "sincere" in their heresy, but the term has nothing to do with sincerity. In theory, I could be 100% sincere, but still be a formal heretic.
Formal refers to the WHY of faith.
Material refers to the WHAT of faith.
So, the correct Catholic formal motive of faith is we believe what we believe because it was revealed by God and then proposed to us as revealed by His Church. In other words, Catholics believe what they believe because the Church taught it. That's their motive for belief, i.e. the formal motive of faith.
There are many in the Conciliar Church who intend, as with the act of faith, to believe everything that the Church teaches, but are simply mistaken about what the Church teaches. As St. Augustine explained, the litmus test for these is that as soon as you tell them what the Church teaches and let them know they're mistaken, they immediately let go of their erroneous belief with the attitude of, "Oh, I'm sorry. I didn't know that's what the Church actually taught." Individuals such as these remain members of the Church, as they clearly lack pertinacious adherence to a heresy despite knowing that the Church teaches otherwise.
Conversely, I could in theory have picked up my Bible and developed a doctrine or theology that's 100% identical to what the Church teaches, point by point ... but, despite believing every single WHAT that the Church teaches, I am a formal heretic because I do not have the correct WHY of the belief. I didn't believe it due to the authority of the Church teaching, but because I came up with it on my own.
What you're trying to appeal to incorrectly is an incorrect notion of what MANIFEST heresy refers to, not material heresy. Even for Manifest Heresy, a pertinacity must be demonstrated. Otherwise, with a simplistic explanation, a mere typo or a slip of the tongue or an episode of brain fogt while speaking would cause someone to forfeit their membership in the Church. Of course that's absurd despite the fact that you had a heretical proposition publicly manifested. You must also have pertinacity to adhere to something that's contrary to the Church's teaching.