One of these is not a reliable ally
Israel, Hamas and Egypt form unlikely alliance against Islamic State affiliateI do not trust Hamas in this deal. At best they are an ally of convenience that is going along in order to get supplies that would have been cut off by Israel and Egypt. In the past, Hamas has allowed Gaza to be used as a base for attacking Egyptian troops in the Sinai and they are constantly attacking Israel. Hamas is motivated by its religious and ethnic bigotry and over time that is not going to change. If it opposes ISIL it is mainly because it fears losing its own despotic regime to another one.
Egypt’s Western allies are worried about the government’s ability to stop the militants.