twoWayFermata = {
  \once \set Staff.caesuraType = #'((underlying-bar-line . "||"))
  \once \set Staff.caesuraTypeTransform = ##f
  \caesura ^\fermata _\fermata
}

music = {
  f'1 \twoWayFermata
  R1
  f'2 \twoWayFermata f'2
  R1
  b'1 \twoWayFermata \fine
}

\new GrandStaff <<
  \new Staff \music
  \new Staff \music
>>