you can run the amp the same or lower impedance.
two 16 ohm speakers run in parallel is an exact 8 ohm load.
you can run the amp on 4 ohms and see a reduced amount of volume but gain a thicker tone.
you CAN NOT run the amp on 16 ohms with the impedance load equaling 8 ohms.
just remember the same or lower for the amp and your fine.