HI jklevela,
I am sorry but I couldn't understant the first part of your question. For the second one, yes there is a way via HTTP cal to your sharepoint site collection to check if the document is checked out or not:
Make a simple get HTTP call to:
https://{base url}.sharepoint.com/sites/{site name}/_api/web/GetFolderByServerRelativePath(decodedurl='/sites/{site name}/{folder name}')/Files
Then will list you all the documents and if you don't know the id or you want to make it more dynamic, filter directly by name or for eah one, check which one your are interested.
The property "d:CheckOutType " eq to 0 indicates this is checked out. For more information (who, when?) extend your call (once you have the reference of the file) with:
Web/GetFileByServerRelativePath(decodedurl='decodedurl='/sites/{site name}/{folder name}')/{file name.extension}')/CheckedOutByUser
Hope it helps 🙂