What's the difference between a Double room and a Twin room?
A double room has one double bed. A twin room has two single beds.

We have two small children; can we get extra beds in the room?
In general one extra bed for one child is available at a minor additional charge. However, please note that this possibility depends on availability.

Can I generally request an extra bed for a third person in a double room and at what costs?
It will depend on hotels policy and availability.