If a Dutch, Afrikaans and Belgium person was locked inside a room for 24 hours, would they be able to communicate with each other easily?

Most of us understand each other without much effort if we speak formally. As Zirp mentioned, colloquialisms/slang/local dialects will be more difficult.

If you are asking whether Afrikaanders, Flemish and us cheeseheads can understand eachother's native languages, the answer is yes to a great extent - assuming we don't speak our local dialect

There is a near certainty all of them will speak English.

Probably if they wanted too.