How to Quickly Insert Pages from One InDesign Document into Another

Hey Steve, this is WAY after the fact, but maybe this will help someone else. You can select pages from one document and then in the page hamburger, select move pages.  Select the open document that you want to move the pages to and follow the prompt. 

Try it out on a duplicate set of files - I'm not the best scripter

Found a script here that looks like what you want

https://stackoverflow.com/questions/57545582/indesign-script-to-add-a-page-to-every-given-page

Haven't tested it properly but I suspect this might work better with a tweak 

var mainDoc = app.activeDocument; // Assuming this is Document A
var insertDoc = app.documents.itemByName("B.indd"); // Open Document B separately

var addPageLocation = 0;  
var docLength = mainDoc.pages.length;  // Start with the original length of Document A

for (var i = 0; i < docLength; i++) {

    // Duplicate the page from Document B to Document A after each page
    insertDoc.pages[0].duplicate(LocationOptions.AFTER, mainDoc.pages[addPageLocation]);

    // Update the page location to skip over the newly added page from Document B
    addPageLocation += 2;
}

Create PDFs of each file. Check out PDFsam Basic, a free open-source program. It can do an alternative mix of the pages. 

https://pdfsam.org/

Write a script, or get someone to write a script. There is no built-in feature in InDesign to do it.