You can prove maintaining H-1B status for transfer purposes and should not face any hurdles on the delayed compensation count.

Yes, parents are eligible to apply for an extension of stay. Need to properly document.

There are both pros and cons which must be analyzed.

Need more information. Need to have a confidential consultation with a lawyer.

I agree. You can join "C" now, again "on receipt."

With this kind of immigration record he will not be issued any visa even after 20 years.

USCIS has up to 120 days after an interview during which to render a decision but could take more. You are free to make inquiries.

USCIS normally cashes the payment within 4 to 6 weeks of having received the extension package.

I agree. This is simply bigamy and you better be forewarned.

You will not lose your EAD because reapplied for H-1B.