Look at the fee agreement you signed. If there was no fee agreement contact the State Bar Association.

You will not be arrested. For their threats see a FDCPA Attorney.

Your neighbor can sue. For your issue, contact a consumer rights attorney.

You can sue the arrested person and the bonding company can sue you. You are responsible for the debt but you can try to find defenses once they...

Yes, you can sue him for his share. Depending on the amount, and your state's laws, you may be able to sue in small claims court yourself.

You can work with the process server to meet them in person.

If they did not say the reason they were calling, it is not unlawful. But, consult with a FDCPA Attorney.

There is no agreement. You did not agree to a critical term, the amount.

There would be a conflict if the attorney had confidential information from you on the first case that could be used in the second case.

If you could provide more details, that would assist in getting the best answer.