Submit two forms to the same page

You cannot do this with pure php. You'll need javascript and write it in a way that when you hit submit on the modal it 'puts' the information back into the parent form.

One way is to make the modal form submit button not an actual submit button.

You might even be able to get away with taking the filled out section dom elements in the modal injected back into the parent form. Some jquery plugins already do this. For example colorbox

Here is a working example using only ONE <form> tag and jquery colorbox. http://jsbin.com/olalam/1/edit

I am not a php developer, so I'll suggest an alternative approach.

Before you refresh the page, you can serialize the form and store the data locally (e.g. in a cookie) then restore the data back into the form. Granted, that will require a bit more JS code, but should get you what you want.

UPDATE: Since you mentioned that you might need a little assistance on the JS front, here is some guidance:

1. Grab the jquery.cookie plugin here.
2. Grab the jquery.deserialize plugin here.
3. Use the following code as a starting point.

.

// the name of the cookie
var cookieName = 'myCookieName';

function beforeSubmit() {
    // serialize the form into a variable
    var serializedForm = $('#id-of-form').serialize();
    // store the serialized form
    $.cookie(cookieName, serializedForm, { path: '/' });
}

function afterRefresh() {
    // read the cookie
    var serializedForm = $.cookie(cookieName);
    // de-serialize the form
    $('#id-of-form').deserialize(serializedForm, true);
}

HTH