FRC and Birth certificate make your case strong and show strong ties to your country. I sent my original certificates. I think it would be better to send FRC original because your brother is your sponsor.
No it is not necessary to send original FRC. However, sending original is advised. As you will get it back from CHC or in other cases you can get a new one from Nadra on payment of fee.
It is for Pakistani applicants so if you are a Pakistani applicant you can get it from any Nadra center. Reading this link can be helpful: http://www.nadra.gov.pk/index.php?option=com_content&view=article&id=11&Itemid=14