Masri turks ??????????? What are you talking about
We only have sunni muslims in egypt (yes that means that every Muslim in the army and police are sunnis that includes sissi himself ) so sectarianism is not the card to play here (it might work in places like syria but not egypt ) but you can...
There might be a third element but if there was a third element they would cooperate (providing money and training)with the mbs as they have a common cause as you mentioned destabilising egypt (as this would mean a bad economy. A bad economy =another revolution)
There is a massive deference between isis and the mbs isis attacks are always much much bigger than this one isis members have lots of experience unlike the Muslim brotherhood they lack the experience of isis. Mbs terrorists cells gets arrested easily so it is a matter of time before the police...