I have Bonifaces in my family, and have done a lot of research on them.
There seem to be two main lines, one in West Sussex and one in East. I am sure that if you go back far enough they may well share origins.
Boniface is a very common name in Sussex, there are a lot of the about. And as Sillgen has said, it is a big county!
If you can give some dates and places, e.g year of birth and place of birth of the Edward Boniface, Stephen Boniface and Leslie Boniface that you list, and a bit more about them, then I will have a look and see if they are ones that have come up in my research.