This is great advice, I feel. I loaned my sister some money for school, and she made an honest effort to repay me, but started falling back on it after a while. So I just said "consider the rest of the loan a birthday present" and asked her to not pay anymore on it.
Because at the end of the day, I'm not going to let money destroy a relationship, and I gave her that money to relieve her stresses, not to contribute to them. So from now on, if I give money to my family, I let them pay it back according to their conscience and ability. People who need money really don't need more things to worry about.
That's the best advice I can see, and it's how I've always done it. I'll never loan family anything, but I'm glad to gift things if I can afford it.
Then if the loan is paid back, you will be happily surprised. But if it’s not you won’t be bitter about it, and it won’t ruin your relationship.
Corollary: don’t lend your family members an amount of money that would cause you hardship if it’s not paid back. (Obviously extreme circumstances call for careful consideration of the particulars. This is not blanket advice)
YMMV.