Sales invoice and daily receipts?

Why would you do that twice? First read the article about daily receipts, it will clarify a lot.

I would remove the daily receipts, since you have already created those sales invoices and sent them to your customers?

Then it is easier to remove those daily receipts, you just have to do it yourself. The sales invoices are already with your customers, so you would actually have to create credit notes... a lot of hassle, easier to delete the daily receipts. Just mention the reason why (required, Dexxter also questions this).

Read the article about daily receipts, that seems like step 1 to me. All the information is there, you just have to read it ;)