Multiplexer and demultiplexer ic

A big difference between analog and digital multiplexers is that the former can be used bidirectionally, while the latter are unidirectional. That means that analog multiplexers can also be used as demultiplexer, while for digital you need separate ICs for that. There are also several types, depending on the number of in/outputs:

multiplexers (non-exhaustive)
8-input: 74HC151, 74HC251,
dual 4-input: 74HC153, 74HC253,
quad 2-input: 74HC157, 74HC257.

demultiplexers (non-exhaustive)
3-to-8 inverting: 74HC138,
3-to-8 non-inverting: 74HC238,
dual 2-to-4: 74HC139.

You can use a pair of analog muxes or an I2C mux (e.g. PCA9544A) to select a sensor (or pair of sensors). You can only access one sensor at a time unless they sit on completely separate busses, so what you will need to do is select one bus, read each sensor on that bus, then select the next bus and read the sensors, etc. until all values are read. To switch the mux, you will either use I/O pins (analog mux) or the I2C bus itself (I2C mux). Just make sure that the mux is set correctly before trying to read from the sensors. Two nested for loops would work nicely, the outer loop will set the mux, and then the inner loop would acces each sensor on the segment.