Here are the joined sentences using defining relative clauses:

1. The pizza that you have made is great.
2. The people who have moved next door to us were friendly.
3. I know a girl whose father is a professional footballer.
4. The man who was talking to my dad is Jenny's coach.
5. The day that finally came was when Brian learned how to use the Internet.
6. The cottage where we spent our holidays was very comfortable.
7. The phone number that William gave to me is wrong.
8. This is the CD that I was telling you about.