Hi Hydie,
It certainly is possible to have multiple signature fields on a form. You can assign each signature to manage different collections within the form as well, so once a person signs, it will lock a particular area of the form. You can even have the last signature apply to the whole form so the last person to sign locks the form entirely. So if you have multiple signature make sure you set which area (if at all) the signature affects.
You wont be able to copy one signature to another as this information is protected against manipulation within the PDF (for obvious reasons).
A single person can sign in multiple fields, but they will have to save the PDF each time they sign.
The PDF will also need to be reader extended for this to work.
Cheers
Darren