A Few Issues Within a Form Page

I currently oversee a website (www.instateangels.com) and there are a couple of things I am trying to do to the page https://www.instateangels.com/start/ which is basically a large form that our clients are asked to fill out. This site was originally built by someone else and now I am adding on features. However on this page I have to ensure the format of a 10 digit phone number (currently it ensures it has no more than 10 digits, but I can’t get it to register an error when the phone number has less than 10 digits), I also need to configure a plugin called SimplePop so that my Pop Up occurs when someone navigates away from the page in any way other than hitting the submit button. I know that this has to be done by changing the HTML class attribute, but I don’t know how to do that. And finally I need a way to have a later field in the page autofill with information provided earlier in the form if a certain checkbox is checked AND the option they choose as a result of that checkbox is Mother or Father.
Please help! I really need to get this done on the site and I really have no idea where to start on these issues!