You can’t make two collections, get both collections to the frontend then sort them in order (even making an order flag etc). If you need an order add an order ID or anything that you can order / sort by and use a sort field in strapi too when retrieving data.
I mean I’m using something similar for a project and that was what I ended up doing.
Though I ended up refactor it to have an endpoint that queries both collections map them together and serves that back.