If that is the case then Mary's mother would, of necessity, have had to be born without sin, since her grandson is the son of God. And therefore, Mary's grandmother ... since the great grandson ... etc. etc. ...
Upon arrival at final step (Eve was sinless) I claim the proof is complete by induction ... therefore, the initial conjecture (Mary was sinless) is proven false.
Male headship dictates that the sin nature is passed down throught the man (Rom. 5:12), not the woman. And if the sin nature is passed down through the man, then there is no issue with Mary giving birth to the sinless son of God.
The questions you ask are ALL answered on the Internet. Please look at Catholic Answers or EWTN or The Catechism of the Catholic Church for correct teaching.
As a note: Romans5: 12 ‘Therefore, just as through one person sin entered the world, and through sin, death, and thus death came to all, inasmuch as all sinned.’ This passage doesn’t teach what you maintain. We know Jesus was ‘conceived’ by the Holy Spirit & was without sin.
Jesus Christ honored his mother as required by the 10 commandments. Theologically, it is possible to believe: The Virgin Mary was redeemed >before she was conceived here on earth. God is eternal. ALL OF CREATION lives in the Heart of God before it is created.
The real question for ALL people when faced with the Truth of the Immaculate Conception is: “WHAT would you do for >your mother????” We know absolutely;> Jesus Christ was without sin & Honored his mother & Father. We are >always being ‘tested’ by God.