For the Treble Clef: Is The "D" played only once and at which value? What is the purpose of this notation?
Such notation shows several voices that you try bringing across with your play in the best manner even if you happen to be short of keys. In this case, the upper voice in the treble clef shadows the melody line of the singer (in the manner of a prompter). If the singer is sure of what he's doing (and there is a singer in the first place), you'll just leave off the upper line altogether. For a-cappella or when helping the singer out, you'll strike the notes of the upper line so that they stand out (or are more subtle) and then should fit the strength of the first note strike into the line even if you are then not going to release the note for a while.
