Passive filter design, transfer functions and loading
It is not necessary to use a buffer between both parts (high- resp. lowpass).
However, there are some specific considerations:

1.) For a bandpass function, the highpass corner frequency must be BELOW the corner of the lowpass - otherwise you get something like a band-stop (notch).

2.) The selectivity (bandwidth) of the bandpass depends on the configuration. However, in any case a passive RC-bandpass has a rather bad selctivity. The maximum Q that can be achieved is Q=Fo/BW=0.5 (midfrequency/bandwidth). This can be realized only using a buffer. Without such a buffer we always will have Q&lt;0.5.