If we want to turn altcoin to cash, will we need to sell it for BTC first, and then send the BTC to service for conversion to USD/EURO before finally to bank?
It depends on the service you are using,for example i use luno and luno supports bitcoin,ethereum and bitcoincash conversion to fiat and straight to your bank account,if you are holding any other altcoins apart from this three you will need to convert them to one of the three first and send to luno wallet to be able to withdraw to bank account