Help adding two totals

Hi There,
ON this page here
http://webpub.com.au/CCS/enrolments/school-fees/
You can see I have used a fee schedule.
Basically the fees change as the number of children at the school change and whether they are in primary or secondary school.
I have one form working great, For one child.
What I would like to do is add another form for the second, third, forth child etc and then somehow get the totals of each of those forms give the grand total....

How do I do that?
Do I have to create 3 or 4 different forms, then somehow get a way to add the total of each form.

If so how do I do this?
A

Ah ok, thanks for the response.
What about having one form with different tables for each child for example so you get a total for each child then have a grand total from all children?

oh man, this seems easy enough but it isn't.
If you select 2 children, then you only want to the two children options to show.
However if you have 3 children you need all 3 to show.
Also if you have 1 you need one to show...but how to I exclude the 2, 3rd children option if only 1 child is selected..

Its getting too confusing...
Do I need to add more questions?