Can three adults live in a standard room in a hotel in Singapore or Hong Kong?

Check it clearly when booking. Some rooms may be ok, but the number is definitely limited. Just making sure. If there is no other way, change to another hotel. Some hotels in Hong Kong are not allowed to have three people in a standard room, but they can sneak in, but if the bed is not big, it will be crowded. Some budget hotels in Hong Kong are not very big. You can find out in advance on some booking websites. I often book Shenzhen-Hong Kong hotels online, which is not bad.