How to get value of checked children checkboxes from checked parent checkboxes in javascript

I have a list of dynamic checkboxes(parent checkboxes) that also have children checkboxes, i want to get only the selected children checkboxes of the selected parent checkboxes.

This is what i have tried:

i used document.querySelectorAll() to get all the checked parent checkboxes, i iterated through each of them using foreach loop, but for whatever reason, i can't seem to get array list of all the checked children checkboxes so i can iterate through them and get their values... this where am stuck. below is the code of what i have done

This is the html code

<div>
    <div class="main-parent">                                 
        <input class="main-checkbox" type="checkbox">   
        <div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
         </div>
    </div>
    <div class="main-parent">                                 
        <input class="main-checkbox" type="checkbox">   
        <div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
         </div>
    </div>
    <div class="main-parent">                                 
        <input class="main-checkbox" type="checkbox">   
        <div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
            <div>
                <input class="sub-checkbox" type="checkbox">
            </div>
         </div>
    </div>
</div>

Below is the javascript code

var test_names= document.querySelectorAll("input[class='main-checkbox']:checked");
    
            test_names.forEach(function(test_name) {
                var testname = test_name.innerHTML;
                var parentdiv = test_name.parentElement.parentElement.parentElement;
                if(parentdiv != null || parentdiv != undefined) {
                    console.log('parentdiv',parentdiv)
                var childtestbutton = parentdiv.lastElementChild;
                
                    if(childtestbutton != null || childtestbutton != undefined) {
                        var childtestprof = parentdiv.lastElementChild.previousElementSibling.lastElementChild.lastElementChild.value;
                        var childtestchecked = parentdiv.lastElementChild.previousElementSibling.firstElementChild.firstElementChild;
                        
                        if(childtestchecked != null || childtestchecked != undefined) {
                            console.log(childtestchecked)
                            console.log(childtestchecked.checked)
                            if(childtestchecked.checked == true && childtestchecked.checked != null || childtestchecked.checked != undefined) {
                                console.log('lengtha',childtestchecked.nextElementSibling.innerHTML)
                                var nnc = document.querySelectorAll("input[class='c-g-t-l-p']:checked");
                                console.log('nnc',nnc)
                                // var array = []
                                // for (var i = 0; i < childtestchecked.length; i++) {
                                //   array.push(checkboxes[i].value)
                                // }
                                // console.log('button',childtestprof)
                                // console.log('childtestnames',childtestnames)   
                                
                            }
                        }else {
                            console.log('box not checked');
                        }
                        
                    }
                }else {
                    console.log('no parent div')
                }
            });

Below is an illustration and snippet;

Thank you in anticipation of your response