Zak: You have several options with how to deal with this. Here are the two I recommend:
1. Sitting your family down for some education about cissexism. Instead of calling them out individually, just mention that you’ve noticed some of them saying things that are offensive and that, while you understand they don’t know any better, you’re giving them a chance to learn so they won’t be as likely to make those mistakes in the future. In order to not sound too harsh and keep things light, maybe make a powerpoint, youtube video, or pamphlet to convey your information. Let them know that you’re not policing language because it’s fun, but because the things they say can sometimes be unintentionally hurtful. Help them put themselves in your (or another trans* person’s shoes) so they can really understand why cissexist language can be bad. A big pro to this method is that it is comprehensive, you only need to do it once (hopefully), and you shouldn’t upset people too much because you’re giving them an overall education instead of calling them out specifically for things.
2. The next time a family member says something you find problematic, take them aside at the next best possible moment and quickly and privately explain to them what you found problematic and why. Try to remain calm and be informative. The best part about this method is that when you call people out individually, you’re more likely to be able to get to each person and address their issues separately. Also, they can’t ignore that you are calling them out, whereas in a group they might think that you’re talking to the rest of the family but not to them. It can be more difficult to keep this chill, though, particularly if the person gets defensive.
There are other options, of course, like leaving educational materials about cissexist language around the house (or giving those materials to your family members with a comment about reading them and watching their language) or writing letters to your family members about how you feel when they use that kind of language. Another option would be choosing a non-threating time and opening up a dialogue with your family members individually about cissexist language and why it is hurtful, and frame it as more of a discussion instead of a call-out. These are just ideas. You know your family best and are the best person to decide how to proceed.