Sub Forms updating Sub Forms

I have created a bunch of forms as a data layer 1:1 without considering dependencies. My plan was to use sub-forms and scripts to manage dependencies before a submission... Let me explain.

<sub-form-1> Section 1 > A bunch of input required (no dependencies)

<sub-form-2> Section 2 > A bunch of input required (no dependencies)

<sub-form-3> Section 3> Input required but must have a 1:M relationship to input from <sub-form-2>

etc... all the way down the list until...{

In between the etc.. There are relationships to map between input gathered from other the other sub-forms in the form

}

<sub-form-7>

So my question is, Can i update subform fields with information from the same form's sub-forms and if so how? I keep getting input type "bigInt" errors and cannot seem to figure out how to dynamically update form data before submission.