you do not need to apply anywhere take your relatives along with your bank Debit/credit card to medical commission and ask your female relative to go in women section medical comm. employees will guide rest of the things inside, likewise send your male relative in male section and same will be done here also, both of them need credit/debit card for medical fee payments Qr.100 each passport. After the medical test wait for sms message from medical commission on your given mobile phone number for test result or check it online at this link. http://www.sch.gov.qa/mcr/En/mcresults.jsp
After medical clearence go to immegration to extend your visa.