The plumber said to me that the cost for his fixing the pipe which is making that cracking sound now in the bathroom would be over $150.

I talked to the old man whose son lives in this house.

The Senator insisted that the president who has complete control over the company be responsible for the bankruptcy.

Although you are eligible to sign up for the class, you were not supposed to visit the office at that time.

As he is an expert in the field, it was no doubt that he could find a feasible answer for the problem.

Please do not try to rephrase or to suggest other grammatically correct sentences but to comment upon those.

Thanks in advance!

Why don't you just say "I talked to the old man, and his son lives in this house." instead?

My intention was to know whether

1) those sentences were grammatically correct conveying the intented meanings,

2) if correct, they have no grammatical issues in using, saying or writing,

3) if not, what made them incorrect by which grammartical rules, and

4) how one should correct them.

I would highly appreciate if someone could answer my above questions.