  We have carried out \textit{ab-initio} calculations of local structure of Mn
and Ni in Mn$_{2}$Ni$_{1.5}$In$_{0.5}$ alloy with different site occupancies in
order to understand the similarities in martensitic and magnetic properties of
Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ and Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Our results
show that in Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ alloys there is a strong possibility
of Mn atoms occupying all the three, X, Y and Z sites of X$_2$YZ Heusler
structure while Ni atoms preferentially occupy the X sites. Such a site
occupancy disorder of Mn atoms is in addition to a local structural disorder
due to size differences between Mn and In atoms which is also present in
Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Further, a comparison of the calculations
with experimental XAFS at the Mn and Ni K edges in
Mn$_{2-y}$Ni$_{1.6+y}$In$_{0.4}$ ($-0.08 \le y \le 0.08$) indicate a strong
connection between martensitic transformation and occupancy of Z sites by Mn
atoms.
