ahh.... the good 'ol "parents doing you a favor" bit. I never had much of an issue with my parents, but when I first started doing this full time my grandfather was very, very bad about telling his 70+ year old friends that I could cut their 1/2+ acre lawns for$15/$20....
Here's the problem. I was raised to honor, respect my elders (you sound similar) and I felt obliged that I had to do so. Honestly at the time I didn't know what my hourly cost of doing business was. I thought if I was bringing in money, I was making money... wrong. I had to have a sit down "man to man" conversation with my grandfather, grandmother, anyone else who was pricing my services for me.
I had to get them to realize, this is what I'm doing for a living! This isn't just something to waste time or to occupy my time. Then finally I had to man up and tell each one of these $15/$20 clients, hey... I'm sorry my family priced this for you, but they don't know what is involved in my business. I'm legal, legit, have insurance, taxes, fuel, payments, etc... I will work with you, but I have to get at least $xx. Most of them were understanding, but there were a few who were still living with prices from the 70's thinking I should be out there with a reel mower doing it for $5 and a Coke.
I have and still do have great parents and grandparents, but when it comes to business I'm the one who writes the checks and pays the bills. They don't. Not being rude, but when someone else has their name on the account I'll listen to them. You have to be loving, but firm.