I don't see anyone getting sued for posting a concert of children playing Christmas music on a facebook page. But, if you're worried about that then I would suggest playing the prepared video online for your parents once. There's nothing against airing a prepared video of your students one time. The worst that a company can do is issue you a "cease and desist order or face consequences" kind of letter. Of course if they do that and you refuse to take down the content from the internet then you're probably liable at that point. I have personally never been contacted from a publisher/ lawyer about any band stuff that I have posted online of my kids performing and I have posted a lot of stuff in all sorts of varieties. I've always been fully prepared to remove such videos if ever asked. Good luck in your decisions.