In Aegean golight if I buy 4 tickets (in golight) how many items of hand baggage can I bring with me?
And again if I buy 4 tickets (we are family 2 + 2) is there any way for me to be sure we are going to be sitting together?
The Aegean website says that golight passengers are allowed one free piece of cabin luggage each:
The only moment in which you can select your seats is upon checking in. Fortunately Aegean allows its GoLight passengers to checkin online up to 48h before departure. Note however that the airline has the right to move you to a different seat if they want to, so guaranteeing that you'll be sitting together is kind of impossible. It's likely though that your selected seats won't be changed unless there's a real need for it.