IF I am doing this correctly, then, there seems to be problems in the
current standalone​ when there are two x-refs to a single heading. The
space after “and” is missing and should the order of the refs not be
alphabetical?

MWE

\starttext
\seeindex{animal}{cat}
\seeindex{animal}{quadruped}

%\seeindex{animal}{whiskers}

The \index{cat}cat has \index{whiskers} whiskers.
\blank[3*big]
\placeindex
\stoptext

Uncomment the \seeindex{animal}{whiskers} and it gets even messier.

Alan