Val, although the registered births which David gave you are earlier than civil registration became compulsory in the IOM, the certs should give both parents, a residence, and occupation for their father, and possibly other details. You can email the Registry to ask about buying copies of these at www.gov.im/registries/general/civilregistry/ See "Contacts" at the top.

Alternatively see: www.gov.im/registries/General/CivilRegistry/family.xml about how to download the Application form to post with payment.

Make sure you give them all the index details and exact date and say you want the Long birth certificate (because it is earlier than usual) or they might think you are asking for their baptism record which usually would have less information than a civil regt cert.
They ask for page and entry numbers for the cheaper price, whereas BL's index gives parish [Douglas] and page numbers [34 for Edward; 28 for William] which along with the parents' names hopefully would be enough.

Sue