Can you see how we are working backwards step by step?
Now you have your greatgrandparent's marriage and the names of both fathers. As Garstonite said, it is more fun and probably easier to follow if you do it yourself. To be really sure you have the correct family you will need to buy some certificates at some point. However, you are lucky as, at the moment you are not dealing with really common names such as Smith!
Shout if you need more help.