@De Maria, I don't understand this, how is Jesus explaining why Mary is His mother by those statements?
For that, we have to go back to Luke 1:38;45
38 And Mary said, Behold the handmaid of the Lord; be it unto me according to thy word. And the angel departed from her.
45 And blessed is she that believed: for there shall be a performance of those things which were told her from the Lord.
Note that St. Luke, writing by the inspiration of the Holy Spirit, depicts Mary as faithfully doing whatever God wills of her.
If then, we read Luke 11:27-28 and understand Jesus to be somehow condemning or denigrating Mary as an unfaithful woman who has not done His Father's will, as the Protestants do, then we are making Jesus contradict the Holy Word of God. And that is impossible. God does not contradict Himself.
Therefore, we have to do what Protestants call to "correlate the Scriptures." Jesus is saying that only the most faithful of people may be related to Him. We can therefore conclude that this is the reason why Mary has the closest relationship to Him. Because she is the most faithful of any creature which God put on this earth. No human has a closer relationship to Jesus than the woman who carried Him in her womb for 9 months and gave Him birth and then nursed Him and raised Him to adult age. No one loves Him more than His mother.
Does that make sense?