Question

A son or daughter will come to visit them. They are expecting this. (join into complex sentence)

Answer 1

“They are expecting that a son or daughter will come to visit them.”

This seems to be the appropriate output when two simple sentences are joined together to form a complex sentence.

For more information on how to join sentences, grammar, sentence construction, other aspects of grammar, visit relevant resources available online.

Answer 2

A son or daughter are expecting to visit them.

Complex sentence is the sentence with 2 or more of dependent sentences as well as independent sentences mixed together by subordinating conjunctions.

Some of the words used for the complex sentences are as "although," "until," "after," "while," or "when'".

Sentence "before" is a subordinating conjunction and the dependent sentence are mainly determined.