Basically I was offered a PhD after my bachelor's degree based only on my performance in the BSc but I enrolled on an MSc and kept this offer as backup. I have been offered another PhD but it is based on the MSc results rather than the BSc results. The second offer are asking if I could accept the offer sooner rather than later, but obviously I don't want to refuse the first offer just yet as I know that it is guaranteed. If I email the second offer and say that I want to accept, would the supervisor who made me the first offer somehow know that I had accepted the other offer and withdraw his offer? I do not want to turn down the first one if I have not received my MSc grades. I assume that different universities would not correspond over this type of thing, but I don't know for sure, and I did tell the people who gave me the second offer that I had already received an offer elsewhere and which university made that offer: is this all confidential or could they inform the people who made the first offer?
Obviously, if I don't meet the conditions for the second offer, I could then fall back on the first offer whose criteria I have already met.