1. Tony's not my brother.
2. Tony isn't my brother.
3. My name's not Peter.
4. My name isn't Peter.
5. This's not my pen.
6. This isn't my pen.
7. That's not my ball.
8. That isn't my ball.
[Can we use all the expressions? What do you think about #5?]
all ok
#5a is syntactically correct, but I've never seen it written that way.
Spoken, it would sound just like "This is not my pen."