Is it possible to interconnect the outputs of 4 ADG406 if only 1 switch of the 4 ADG406 is switched?
Yes, you can. But, bear in mind that the parameters of this new configuration will not be the same as in the datasheet since that is for a single ADG406.
In this case, you will have added capacitance and leakage in your system. Also, you will need more digital signals to control your new configuration, however, this can be simplified by just controlling the EN pin of each ADG406 individually and having A0, A1, A2, and A3 common to each switch.