Is there any danger / risk having my bitcoins at poloniex after 1. August ? Also will my current Bitcoins remain Bitcoins (and not BCCs or a mix) at poloniex and bittrex after 1. August ? Cant find the answer anywhere !

You dont have to take that risk. You can always withdraw your coins in a desktop wallet like Electrum and have them held there safe on August.
Thats what everyone should do.