Please correct my english

[malta22]

Are these sentences right?


The children have been happy since their dad has returned home.

She knew that I could have already checked the homework.

[Barb_D]

Are these sentences right?


The children have been happy since their dad has returned home.

She knew that I could have already checked the homework.

For the first one, "since" works better when you refer to a specific point in the past - the date when their father returned home.
The second one is possible. What situation do you mean to describe?

[malta22]

Thanks Barb D for you reply.

The second sentence shows a situation.

Someone had a difficulty about the homework. She called me late in the evening because she knew that at that hour my homework would be already done.

[Barb_D]

Then I suggest you replace "could" with "would" in your sentence, and replace "checked" with "completed."

She knew that I would have already completed the homework.