The term multiplexed in this case means the pins used for the EUSARTS are also used for other functions - it does not mean that both EUSARTS uses the same set of pins.
EUSART1 is mapped to RC6 & RC7 as you show in the datasheet. EUSART2 can be mapped to any of RPx pins of the device. Read thru section 9.7 of the datasheet for further details.

I've never seen this functionallity in a PIC before, thank you for pointing me to it! Looks extremely flexible!

/Henrik.