Young is such a common name. It is really hard to tease out the information, it is like looking for a needle in a haystack. That is why it has taken six years to find information on the Young branch over on my side and even then I think I have found very little. I would say that ancestry.com is your best bet. Even though it's expensive, I have to bite the bullet and join as I need it all the time for my work now. Also look in both country's electoral roll records online (again both through ancestry). You can kind of work out whether you have the right people and their movements by opening more than one window and comparing records. Also Mundia is turning out to be a newer but excellent resource for family tree info.
Since then I've found more Youngs so we have them coming in from four different places but seemingly all unrelated families. Looks like you found your twins in the end and even got photos. Well done. If you get tricky with BDM you can work out quite a lot and also Mundia has turned out to be one of the best resources for finding info. Also Archway can be good. Cheers dz