Will the I2C devices respond to I3C commands?

No. The I3C CCCs are always preceded by the I3C Broadcast Address, 7’h7E. Since the I2C specification reserves address 7’h7E, no Legacy I2C Target will match the I3C Broadcast Address, and thus no Legacy I2C Target would respond to the I3C commands. Likewise, the Dynamic Addresses assigned to I3C Devices would not overlap the I2C static addresses, so no I2C device would respond to any I3C address – even if it could see it.