Hello Luigi
1.-
These registers were not designed to work at the same time so they have no configurable pyrity, simply if it is in tri-state it will be in high impedance no matter what else.
You can find more information in the datasheet:
8.10.3 Tri-state SP register
The tri-state command is use to set the input nodes as high-impedance (Table 13). By setting the tri-state register bit to logic [1], the input is high-impedance regardless of the Wetting current setting.
2.-
The output current on AMUX will be pulsed, I mean, the wetting current will be applied only for the first 20 ms, and then reduced to the holding current (2mA)
I hope this information has helped you, please let me know if you need help with anything else.
Have a great day and best of luck.