Dont book anything before you go is my reccomendation..
I know it sounds cheap when you look on the internet, but If you book accomodation over the internet, you're asking to get ripped off.
Looking at the name of your hotel, you may get scammed as Ao Nang and Krabi beach (more like mangroves) are about a 30min bus ride apart, with TonSai (where most of the cimbing is) about halfway in between them, but only accesible by boat.
So you might rock up at AoNang and find tht infact your hotel is in krabitown... not quite as nice, or on the beach as AoNang...
Ton Sai is also a longer (read more exposed if theres a bigger low season swell) boat trip from krabi.
How old are your kids? If they can manage in a bunglaow by themselves, stay at TonSai in a bungalow each. I'm not sure abot family rooms in Ton Sai, but from memory last year at dream valley they were building what looked like massive multi-room bungalows.... probably still cheaper than a hotel...
Hope this helps, sorry about some vaugeness, going off memory.