hotel rooms occupancy in South Korea

Hi

We have been trying to book hotel on line for our trip in South Korea but almost every hotel that we choose dont have triple occupancy option on line.

We are party of 6(me,husband, 12 and 16 yo,my mum and my aunt)

Can we just book 2 rooms then show up with 3 in a room(extra person hide behind,hehe) or we better email the hotel to see if they have any different offer?

Thank s for any input.

pimple