Let's start by distinguishing between the range where you
want proper function, and the range where you need to
guarantee survival.
Then, your desired gain of the difference signal, and the
output signal swing (range).
Then, the tolerable loading of the input source (because
a resistor divider (pair), throwing away 50% of signal up
front could fix the whole thing?). Presuming that the source
can't itself be convinced to reduce its swing, and that the
entire range has useful information to be processed.
I think I've seen papers on making instrumentation amps
with less than three amplifiers but can't recall where, or the
suggestions. Also 3-amp InAmps can have problems in low
supply voltage circuits and high signal, headroom-wise.
Do you consider the possibility that I/O devices and a
higher working rail could also be a solution, post-scale
if needed? Or is there only one, low voltage supply?