I think you're going to run into problems in Web2py since even if you use Custom Forms (http://web2py.com/books/default/chapter/29/7#Custom-forms) you're going to have two conflicting security keys (hidden fields to prevent CSRF attacks).
If you're able to paint the form correctly in the view, then you're going to need to write most or all of the processing and db updating logic in your controller. There might be a Jquery based approach which works better. Perhaps you could have a Javascript function post back the two forms individually to controllers designed to handle each. Sorry not more helpful.
