Cascades instrumentation amplifiers with a buffer in between stages: What should I use for buffer?
I have never seen a reason to cascade two instrumentation amplifiers.  An instrumentation amplifier takes a differential signal as input, and transforms it to a single-ended ground referenced signal (with most of the common mode noise attenuated).  Once it comes out of the instrumentation amplifier, you can and should just use operational amplifiers for subsequent stages.

What the steps between the Instr. Amp. and the final output are depends upon what your signal looks like, and why you need to use a two stage approach in the first place, when IAs can provide very large gains all by themselves.  Often, you do this because there's a DC offset that you need to remove, and if you amplify in one stage, you'll just saturate the amplifier.    If this is the case, I like the instrumentation amp to provide modest gain, big enough to amplify but small enough not to saturate, and then on the output remove the DC with a high-pass filter (or with a potentiometer or subtraction circuit, if you need the low frequency response), and then amplify more with a noninverting amp.