Can a Multiplexer be used as a Demultiplexer
The datasheet shows that the 74151 is a digital multiplexer:

In particular, it includes internal logic that buffers one of the inputs as a TTL-level output on the output pin, and as a result, it cannot be used as a demultiplexer. Attempting to apply a low-impedance source to the Y pin may cause damage to the source or the pin's driver.
You will need to use a digital demultiplexer, or an analog mux/switch such as the 4051.