I am a dentist. Should I keep providing free service to my brothers and sisters-in-law?

I've always provided free dental care to my brothers and sisters-in-law along with their wives and husbands. When I say free, I mean I usually just take what the insurance gives and don't ask for co-pay. I've never minded giving them free dental care. But now I don't know if it should still do this for them. First of all, two of my brothers-in-law cancelled their insurance because they realized that I'm not going to charge them. So now its not that I only don't get co-pay, but I don't even get insurance pay. This was still fine for me, they are family. But the thing is that they don't even show much appreciation. They never even ask me if they should pay. Nor do they ever show some gratitude with a gift or giftbasket or anything. Now please realize, I am NOT asking for a gift or I am not working for free so I get a gift. But at least they should show some sort of appreciation and shouldn't just take me for granted am I right?
--------------------
of course not !!!
Source