If the sampling rate is not an issue, I would suggest to put the 4051 addressing on a GPIO extender such as MCP23017, it is an I2C chip that can be controlled from the ESP8266 using only 2 of its GPIOs, providing new 16 GPIOs, where only 3 is needed to be hoookup to the 4051, the remaining can be used for any other ideas we can have ...
Dunno if rf interfere with all adc though.