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 Unzaga died in 1790.
Luis De Jesus's birth name is Luis Angel De Jesus.
Fernando De Luis's birth name is Fernando de Luis Molpeceres.
Luis Vaez De Torres is Spanish.
Luis de Miranda was born in 1971.
Luis de Montesinos was born in 1552.
Luis de Montesinos died in 1620.