Building a Bio-impedance system
Apparently, they use at least 2 frequencies with a current source and measure the voltage as impedance.  The current is only 1~10uA and f1=10k~100kHz f2=1~10MHz.
You can multiplex the signals with analog Mux.
https://academic.oup.com/ajcn/article-pdf/64/3/388S/24035357/388s.pdf