Multiple slurs between chords

[Joel C. Salomon]

Below is a minimal excerpt from an attempt to typeset the piece where
the attached image is taken from.

The way I’ve written the lower staff is (I think) more “correct”
according to the voices in the piece, but there is only one slur line
between the chords.  The way I’ve written the upper staff gets me closer
in looks to the printed version, but not quite correct either.

    \version "2.19"
    \language "english"

    upperOne = \relative c' {
        \voiceOne
        e4.(                    d4)             %…
        \oneVoice                               r8      |
    }

    upperTwo = \relative c' {
        \voiceTwo
        cs4.(                   d4)             s8      |
    }

    lowerOne = \relative c' {
        \voiceOne
        s2.                                             |
    }

    lowerTwo = \relative c' {
        \voiceTwo
        <a, g'>4.(              <d fs>4)        %…
        \oneVoice                               r8      |
    }

    \score {
        \new PianoStaff <<
                \new Staff = "upper" <<
                        \clef treble    \key d \major   \time 6/8
                        \upperOne
                        \new Voice \upperTwo
                >>
                \new Staff = "lower" <<
                        \clef bass      \key d \major   \time 6/8
                        \lowerOne
                        \new Voice \lowerTwo
                >>
        >>
        \layout {}
        \midi {}
    }

(In the [attached] larger file, I was able to put an explicit \oneVoice
overriding \voiceTwo and imitate the printed version, but this only
worked for the upper staff, and not in my excerpt.)

Can anyone suggest the correct way forward?

—Joel C. Salomon

Slurred Chords.png
Description: PNG image

PP03_Lullaby.ly
Description: Text Data