Here are the combined sentences following the structure "subject + be + adjective + that-clause":

1. She is certain that her son will be accepted to a high school for the gifted.

2. My father is upset that my brother wants to drop out of high school.

3. He is amazed that his colleagues celebrate his birthday in a fun way.

4. She was worried that her father's surgery would be unsuccessful.

5. We were relieved that the rain had finally stopped.