  We study three-dimensional time-reversal-invariant topological
superconductivity in noncentrosymmetric materials such as RhSi, CoSi, and AlPt
which host coupled multifold nodes energetically split by the spin-orbit
coupling at the same time-reversal-invariant momentum (TRIM). The topological
superconductivity arises from the $s_{+} \oplus s_{-}$ gap function, which is
$\boldsymbol{k}$ independent, but with opposite signs for the two nodes split
at the same TRIM. We consider various electron-electron interactions in the
tight-binding model for RhSi and find that the topological superconducting
phase supporting a surface Majorana cone and topological nodal rings is favored
in a wide range of interaction parameters.
