May I book a standard room for our family of three? There are no family rooms available, and the standard room says it can only accommodate two adults, but my daughter has just turned 18 this year ?

Sure, we stayed in a standard room for four last time. He just charges according to the actual number of people for breakfast.

Check the hotel's requirements. How many people can stay in each room? Is it allowed to add a bed? How much does it cost to add a bed? There are rules. If two people book a standard room and three or four people stay without informing, the consequences may be very embarrassing. There is no need to do this when you drive out. In March, I went to Germany, Italy and France. It was three of us. When searching for a hotel, in addition to time and location, I had to add the search condition of three adults.

I suggest you contact the hotel by email first and ask for permission to check in. Otherwise, the hotel has the right not to let you check in. My friend was forced to check out last time in New Zealand because he didn't inform the hotel in advance.