Posted: 07/10/2013 at 21:27
Well, top marks for trying, aes!
Having said that you are a novice gardener you are just about to try a technique that most gardeners leave to the professionals.
All apple tree varieties have their own particular shape and degree of vigour so that might account for the difference in the two trees' shapes now. However, and it is a big however, they belong to two different pollination groups. This means that the St Edmund is one of the earliest to flower and Newton's Wonder among the latest. Hence, they are never going to pollinate each other.
So, if you were to graft yet more varieties onto one or both of them the grafted varieties would need to correspond in pollination group with the plant onto which they were grafted. All getting a bit complicated.
Are you short of space? If not, I would advise against grafting. It is a skilled job and you could well create more problems for yourself. I would advise you to go to a good garden centre and buy two more trees, one in pollination group 2 for St Edmund and one in pollination group 5 for Newton.