  We perform \textit{ab initio} investigations of the bulk and surface band
structures of LaSb and LaBi and resolve the existing disagreements about the
topological property of LaSb, considering LaBi as a reference. We examine the
bulk band structure for band inversion, along with the stability of surface
Dirac cones (if any) to time-reversal-preserving perturbations, as a strong
diagnostic test for determining the topological character of LaSb, LaBi and
LaSb-LaBi multilayer. A detailed \textit{ab initio} investigation of a
multilayer consisting of alternating unit cells of LaSb and LaBi shows the
presence of band inversion in the bulk and a massless Dirac cone on the (001)
surface, which remains stable under the influence of time-reversal-preserving
perturbations, thus confirming the topologically non-trivial nature of the
multilayer in which the electronic properties can be tailored as per
requirement. A detailed $\mathbb{Z}_2$ invariant calculation is performed to
arrive at a holistic conclusion.
