Easyjet customer service finally replied to my email. In case anyone else runs into the same question, this is what they said:

"I would like to confirm that the luggage fee covers both flight segments."

I'm not sure if it is because I booked both flights on the same PNR or if because Venice is both the arriving and departure city, I only have to pay for the luggage fee once. So their automated email that I received is correct that when I paid for 2 pieces of luggage, I am allowed to have 2 luggage on both segments.