Your problem is not that your family is conservative. I don't know how "bad" your GPA is, but if it's trending downward, the problem is not your aunt/grandfather's views on the world, however outdated they may be. You don't necessarily need to change their view on programming / open source, but you should appreciate they are concerned for you, possibly for good reason.
pg has a PhD in computer science from Harvard. Do you think his undergrad GPA was low?
You have four years to get a decent GPA, you have your entire life to contribute to open source. You can possibly do both while in college, but the former might be more important.
Once you get past the point that people care about your GPA, no one cares about your GPA.
You might need that GPA to get into a competitive academic program, to secure a research grant, to add another string to your bow when you try to convince an accelerator that you have the smarts to back up your charm and creativity, or simply to get a job at a competitive company.
No one cares about your GPA once you get past that point. That point is not necessarily graduation.
A low GPA can keep you out of a good grad school. (A low GPA can keep you out of officer school, if he wants to join the military as an officer.) 5 or 10 years down the road, yeah, it doesn't matter. But for his very next step after graduation, it probably does. (And next steps lead to next-next steps which lead to next-next-next steps.)
On the flip side: Linus Torvalds inventing Linux, or Guido van Rossum inventing Python has, I'm sure, benefited their own careers. I'm totally down with doing the "crazy, hippie, open-source thing" because it's your passion.
But: I'm guessing that Linus and Guido (and pg and others...) all did very well as undergrads. If you're destined to be an open-source badass (or a startup badass), then 4 years of good grades shouldn't be too painful.
(And, I'll just say it, anecdotally: finishing my physics degree made me into a smarter, better person. At the time, my quantum mechanics classes were the hardest things that I had ever done in my life. And now, my own hobbies are just as hard... and rewarding.)
edit: I'd like to mention that I didn't graduate college until I was 28. I can totally empathize with following an unusual path in life that your family doesn't approve of.
For one thing, he might not graduate at all. Ok, so he has his open source credentials. That might get him a job or give him connections to help start a company. But a bad academic record is not a positive indicator you are an open source genius awesomedude. Rather, good contributions to open source can make up for a bad academic record in the past.
Who knows, maybe the particular college is a bad fit, and there can be a million other problems. But explicitly sacrificing GPA for amorphous contributions to open source is like tithing when you can't feed yourself or your own family.
Maybe my own experience is outdated or not generally applicable, but one's grade in a computer science class is fairly indicative of how well you grasped the material. It is precisely the classes I did well in that I haven't needed to restudy (and vice-versa).
That's just absolutely not true. What is true is that not everyone in every situation cares about GPA. Also true is the idea that your GPA matters more and more if you on the extreme side of things (very high or very low). Someone who graduated Magna Cum Laude from Harvard, for example, will want to show that to prospective employers even if they are 55 years old. Someone who graduated with a 2.2 from Podunk U will try to hide that even at 23 years old.
Who knows what will happen to OP over the next 10 years? Who knows what opportunities s/he may be in that would or would not require GPA disclosure? You don't. I don't. But to tell an unknown person who you know only 2-3 sentences about that "noone cares about your GPA" is just irresponsible. Perhaps no one cares about your GPA but those are reasons unique to you or your life.
pg has a PhD in computer science from Harvard. Do you think his undergrad GPA was low?
You have four years to get a decent GPA, you have your entire life to contribute to open source. You can possibly do both while in college, but the former might be more important.