I agree with those that suggest contacting one of your sisters and just laying out what you've said here.
It's come to my attention that the family is asking some of my friends on FB for information on my whereabouts. I now realize that I at least should let you all know that the kids and I are fine and we are safe. Right now, I will not be in contact with anyone in the family and I will contact you again when I am ready. I have put thought into this move and am not doing this lightly. This absense was well planned. I will be in touch again, but in the meantime, please do not ask my friends for any additional information. I have asked them not to say anything and they are uncomfortable being in the middle."
Also, if you are comfortable, since you said you wish to establish contact with your sisters again someday, it might be good to give them at least an email address that they can get news to you through. In case you want to know if there was a family emergency, or the sisters move and they can keep you with udated contact info. You can tell them that you won't be replying to the emails until you are ready, but if they do need to pass on some info to you, that you will be reading them...you can also let them know that you aren't interested in any drama that ensues, so if they decide to pass that on to you, you may choose to cut off that contact as well.
I have no experience with this, so take my suggestions with a grain of salt if there's some ramification that I haven't thought of.