Do you have attire matching a satanic witch? If so, to best illustrate yourself, I would suggest you to put this attire on so your family better understands.
If there are any customs or, uhhh, rituals... Maybe performing one or two will help also.
If you're in a club or organization... Maybe you should bring some or, heck, all of them in your traditional attire. Ensure everyone is behaving as properly as they can, of course, to that which a satanist witch would uphold as proper behavior.
I believe this will help detail to your family, your convictions and goals.
Could you also let us know how it turns out?