Yes. You will need barcodes if you are selling to a retail or online store.
One for each album title. If you change anything about your album, it becomes a different album and needs a different barcode.
That depends on the retailer you are selling through. Some allow you to use the barcode number from the complete album. Some may require you have to have a barcode for each individual song. You would need to find out what the retailer’s requirements are before purchasing the barcodes. If they want you to have one barcode per song, and you have 10 songs on your album, then you would need 10 barcodes plus 1 for the complete album.
You can put the two albums together and sell them as one item, so you will need one barcode. If you change out either one of the albums it becomes a different product and will need a different barcode.
You can use the barcodes an unlimited amount of times as long as it is on EXACTLY the same product. The minute you change one thing about your product it becomes a new product and needs a different barcode number.