How can families persevere in practicing forgiveness? My worry within my own family is that as I introduce the idea of forgiveness, people may get initially excited and then it just fades away.

Perseverance in the practice of forgiveness takes a strong will.  Do you have that strong will to quietly and gently and without force keep the message alive that you value forgiveness and would like it to be a part of your family?  As an analogy, starting a fitness program is good, but continuing with it is even better.  How do people continue?  They establish routines; they enjoy the kind of exercise that they do; they create an expectation for themselves to continue.  The same can occur with becoming forgivingly fit.

For additional information, see:  Learning to Forgive Others.