You two need to do a bit more research. Why would there be a military coup? The country has been under martial law since 1981 - the military already runs Egypt.
I'm not an expert on either Egypt or the MB, but something tells me the Egyptian military wouldn't like being forced to live under Sharia Law any more than other non-MB Egyptians would. So if the military's only choice was an MB government or a coup, they might opt for a coup.