Rachel my

is that they are your family and they will love you no matter what they "think" of you. Slow and steady. Allow them plenty of time to accept your view but be prepared to accept that they may never
agree with your decision. We can hope that they
respect that
it is your decision.
Knowing your facts is important. Being self-confident in your beliefs is better. Resist the desire to always be right with them as waving a debate at them every time you see each other risks driving a wedge into relationships.
By all means try to get them to the range. Start with your sister. I'm going to guess one range trip would have more positive influence than 100 kitchen table style gun debate fight songs. That's my armchair counsel for the day.
