Hi,
If you want to make a two stage totally passive filter behave similar to a two stage with a unity gain amplifier in between (to achieve impedance isolation) then the usual idea is to make the impedance of the second stage 10 times the impedance of the first stage, but keep the dual single stage break frequency the same.
This is very easy to achieve because the break frequency is proportional to R and C, and to increase the impedance of the second stage we increase R. This also leads to decreasing the second cap value since we increased the second R.
So for a passive circuit with R1, C1 as the first stage and R2, C2 as the second stage, the values for the second stage are simply:
R2=10*R1, and
C2=C1/10
This makes the break frequencies of both sections the same but keeps the second stage impedance 10 times higher than the first.
This really works for any ratio not just 10, but 10 is considered to be a good minimum and anything higher than that is great.
For a bandpass however, there is also the thought about the bandwidth and that means we might want to shift the high pass section break frequency a little higher so we get wider bandwidth (if that's what we really want). This would simply mean changing the values of the second stage (HP) so that the break frequency is a little higher, and the best way to do this would be to lower the value of C2.
Of course we also have to think about the input driving impedance and the output load impedance. The input drive impedance acts as a series impedance that would be in series with R1 (R1 and C1 make up the LP section), and the output load impedance acts in parallel with R2.