Splitting voices

[E Appeldoorn]

I have a score consisting of 5 strings. Near the end all instrument 
voices (except the bass) split into two. The top voice being a solo, and 
the bottom one the rest. I have managed this for one voice, but can't 
figure out how to add second violin, viola, and cello in the same 
manner, then adding the single line bass below that. Here's what I 
created.
All voices would need to be in the main group, Any help would be much 
appreciated.
Erik

\version "2.22.1"
\score {
  <<
    \new PianoStaff \relative c'' {
      \set PianoStaff.instrumentName = \markup { tutti Vln.I}
      \set PianoStaff.shortInstrumentName = \markup { Vln.I}
      \new Staff {
        c1 | c | b | a | g | f | \break % intro
        <<
          {
             \set Staff.shortInstrumentName = \markup { solo }
            c1 | d | e | d |
          }
          \new Staff {
            \once \omit Staff.TimeSignature
              \set Staff.shortInstrumentName = \markup { others}
            g1 | f | e | d |
          }
        >>
      }
    }
  >>
}