Question

He sent his children to -their aunt's- house. (Special)​​

Answer 1

Where did he send his children?

Whose children did he send to their aunt's house?

Who sent his children to their aunt's house?

Who did he send to the aunt's house?

Whose house did he send his children to?

Whose aunt's house did he send his children to?

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For more information:

When did he send his children to their aunt's house?

Why did he send his children to their aunt's house?

Answer 2

The sentence "He sent his children to their aunt's house" uses hyphens to set off "their aunt's" as a special or emphasized phrase. This can be used to draw attention to the fact that it was their aunt's house specifically that the children were sent to, or for some other stylistic purpose. However, it's more common to use quotation marks for this purpose. So, the sentence would look like this:

"He sent his children to 'their aunt's' house."

Alternatively, you could use italics for emphasis:

"He sent his children to their aunt's house."