Thanks for your prompt reply.
We thought that might be the case as they're his children whether my partner marries or not.
The only doubt we have is that - "Do i automatically become their "Step Dad" on marrying their mother?"
I've got no qualms about that and get on with all 3 children brilliantly. They live with us full time and stay with their father every other weekend.
We think we've heard somewhere that if I automatically become their Step Dad through this marriage, then that may effect the maintenance payments etc.
Just one more question; You mentioned in your reply about 19% of gross income. I'm assuming that this has been calculated on having 3 children and that the percentage changes depending on the number of children.