4 pax in a HK hotel's superior room?

I have been searching throughout the Internet and going to Matta Fair for more information on Hong Kong. Yes, another DIY tour!!!

My in-laws, hubby and I are going on a free-n-easy tour on our own to Hong Kong since I manage to get cheap air ticket of RM360 per pax including seat allocation and 15kg luggage checked-in.

We are going to share our room in Hong Kong. I have book a room with 2 double bed in Mongkok, Hong Kong. I'm not worry about the bed size since I've check it out on Tripadvisor, the beds are larger than most Hong Kong hotel's single bed.

What I worry most is the fact that all the hotels only accommodate 2 person in a room, will only allow 1 more child to be in for most case. However 4 of us are going to stay in a room! I doubt the management will kept quite about it. Hubby and I planned to check-in with just 2 of us, follow by my in-laws sneaking in later.

What do you think? Have you stayed in Royal Plaza Hotel, Hong Kong? What would you say about it?

* $$ is the main reason we share a room but it is also due to my MIL fear of haunted hotel room!