I help people for free all the time, and sometimes they help me in areas they're more skilled in. Blood has nothing to do with it. What gets me are these ones who make a business of severely over charging to do the simplest thing because someone doesn't know better. A fair price go for it but when all you have to do is install their OS from a disk they hand you and you charge 200+ it's just being an ass.
If I were a mechanic whose hobby was working on cars, none of my friends/realtives (other than like my mom) would think it would be ok to ask me to do work for them for free. Sitting in front of a computer for 4 hours trying to remove all nature of malware and viruses without losing personal data isn't what I'd consider fun.
I usually just say I'm busy or something, but damn.
My uncle knows a bit about cars and has spent hours trying to fix my mums car. Multiple times.
I think if you think like that you might have some selfish actions hidden deep inside.
you should never let anyone in your family know how good you are with the computer ..
they'll ask for your help every time they have a tiny problem.. you'll end up helping your whole family and then the news will reach your aunts and cousins that you're good with computers and they'll ask for your help ...