Tyresson2012, without actually doing this type of search in person at one of the main genealogy centres, it is tricky as you cannot view any birth cert online (100 year privacy rule). Doing this search in person, lets you view these certs in detail on the terminals there. By this time you can also search (in person only, not online) using mother's maiden name which obviously helps too.
One thing you can do though on the main online index is look for sequential numbers on the register. With twins, you would expect the numbering to follow. There are two Boyce births, both boys though, in the Glasgow area in Camlachie in 1954. Not sure if they connect with what you are looking for. I will send you a personal message with their names and refs.
Monica
