You won't have to go through security twice. Once you have cleared Schengen entry formalities you'll be in the Schengen travel area, T1. I'm trying to remember if the TAP Premium lounge has showers, but I don't think it does. There may be a PP lounge in the terminal that has showers, but I doubt it. I think you'll probably have to wait until you get to your hotel in Barcelona.

Edit: I've asked a moderator to merge this with your existing thread:

Best Lounges flying TAP J in EWR and LIS