汉译英:这屋子可容纳20人

This room can hold 20 people
people是个集合名词，单复数一样，不加S
Who are these people?
这些人是谁?

This room can hold 20 people.

This room is able to hold 20 people

This house can accommodate 20 people．
（其实在google上有翻译字典的，你去看看）