How can I call up a form from inside another form?

You may use the iFrame widget to embed a form inside another one, please check the following guides that will help you with that: 

https://www.jotform.com/help/401-Where-to-Find-My-Form-URL 

https://widgets.jotform.com/widget/iframe_embed 

https://www.jotform.com/help/252-How-to-Add-a-Widget-to-Your-Form 

I hope this helps.