Luis being a proper name, then "in Luis' class".
there is no name for it in English because Spanish name it!
No
What does Elena think of Luis.
De tu means: of your in English.
The indefinite article "de" in Spanish is analogous to the indefinite article "of" in English.
Luis De Jesus's birth name is Luis Angel De Jesus.
Fernando De Luis's birth name is Fernando de Luis Molpeceres.
Luis de Unzaga died in 1790.
Luis Vaez De Torres is Spanish.
Luis De Jesus is 4' 3".
Luis de Castresana was born in 1925.
Luis de Lossada was born in 1681.