SAEguy,
First of all, giving up alcohol for Lent is pretty impressive and I would think that all of your brothers would be very supportive. One of the Irish guys on my boyfriend's soccer team did the same thing this year. I just gave up Coca-Cola!
At any rate, I wouldn't worry about your brothers' reactions. There are plenty of Greeks who don't drink, who are very active in their organizations, are well-respected by their brothers and sisters, and have a good time at events where alcohol is served. I seriously doubt that your brothers will give you a hard time.
