Degu Ethical Dilemma Please Help?

My wife and I have a newborn on the way and she says my Degu collection has to go. I have 6 in total which I have cared for over the last 2 years. There are 4 females and 2 males. I must admit they are cute and I've grown pretty attached to them. I attempted to give them back to the pet store but apparently that is not an option. I live on the small Hawaiian island of Lanai and I'm afraid if I let the males and females go together they might overpopulate the island. We are a small community and the neighbors would know exactly who to blame on that one. I've decided that I'm going to have to put down one cl and let the others go free. My wife says its a no brainer and should put down the males because there are less of them. On the other hand the females have always been anti social and more high maintenance. Am I being unreasonable? Also I'm going to have to do the "deed" myself. I'm trying to find the most ethical way and since degus are natural diabetics I figure a couple gummy bears each should do the trick. Once again my wife is arguing that I should do it quickly by getting a rock, pillow case and dropping them in the sea. I'm open to any better suggestions? Thanks