Are they correct?
1 Your son had better be here. Mine had better be elsewhere.
2 Your son should become a doctor. Mine should become a teacher.
3 I have a pen and a book. The pen is mine and the book is yours.

Thanks!

Question

Are they correct?
1 Your son had better be here. Mine had better be elsewhere.
2 Your son should become a doctor. Mine should become a teacher.
3 I have a pen and a book. The pen is mine and the book is yours.

Thanks!

Answer

1 is fine, but a little stiff. It is simpler and more powerful to say "Your son had better be here; mine had better not be."

2 is perfect.

3 seems to contradict itself, as if two people both own the same book. "I have a pen and a book here" would be better, 'have' now clearly doesn't refer to ownership.

Answer

Perfect :D Great sentences. It sounds like two mothers talking

Answer

hmm.. but to be sure the meaning is correct, what is the situation of no. 1?
No. 2: 'should be' is natural, not become. 
No. 3: to be clear you should say:  I have a pen and a book here. 
:)