Thanks everyone who posted in response to my eating disorders question. It helps hear your opinions and suggestions. My girls get such a limited time with their dad anymore, and with this going on at his house it has created even more "issues" to deal with. I'm just clueless about the "right" way for me to handle it - mostly because I'm definitely lacking knowledge about the topic, and secondly, because I don't want to step on their dad and step-mom's toes. I wish they would be more open and up-front so that my girls would feel they could express their feelings to them.
Again, thank you for the site recommendations and the advise on how to approach it.