Question tags in sentences with "let"

Question

Let them stay here

What is the correct question tag for this

1) will they?
2) will you?

My grammar book is suggesting first question tag, but I think second is correct. Please, help me with this.

Answer 1

Let them stay here is a sentence in the imperative mood, which is used when a command or request is being given.

The subject of imperative sentences—the person to whom this command or request is being given—is normally you (either singular or plural), although it's often left unstated.

In the sentence in the question, the command is being given to you, so that is what the tag needs to be:

✔ "(Hey, you!) Let them stay here, will you?"

Compare that to the alternative in the question:

✘ "(Hey, they!) Let them stay here, will they?"