I didn't have to tell my family because there are people in my family that have noticed me on the internet. After that happens, the word spreads around to everyone else in the family and before you know it, the entire family is aware of it. However, working in porn is not something that I am ashamed of so I really don't care that they know.
The funny thing about it though is that once someone from your family asks you about it, (that is, if they notice you on the internet) - they are admitting to you that they look at porn...and if they enjoy looking at porn sites, how can they get upset with you for working in an industry that feeds their desires?
That is, unless they are hypocritical.
That's just my personal situation though. As far as your situation, if you are not actually featured in the porn that you are working with, you could always deny it and say that those files conisted of a zip download that you downloaded from Limewire and that you never got around to deleting them....or something along those lines. Although, it sounds like you already admitted everything to your cousins and 3 other people.