I like how you referred to the "team effort" involved in co-parenting your daughter.
It's important that everyone involved with your child's care be on the same page. Lots of communication and collaboration is needed. Otherwise, you run the risk of having incidents like the one you described in the original post, and having your child playing both ends against the middle.
If you don't mind my asking (if you do, then don't feel compelled to answer), what is your custody arrangement with him? Are you sharing custody? Do you have primary custody with him having visitation on alternate weekends?
I get the feeling from what you describe that he is leaving you out of the loop in an attempt to undermine your parenting. The fact that his wife has taken it upon herself to teach your daughter the facts of life without first communicating her intentions to you is also somewhat disturbing. Do you ever get the feeling that they are attempting to alienate you from your daughter? They make decisions about getting your daughter's hair cut - again without communicating their intentions to you, claiming that there is a certain "look" that your 8-year-old is trying to achieve. I don't know too many 8-year-olds who care that much about their "look". I can see it when they are teens, but not at 8.
Have there ever been any subtle or not-so-subtle remarks about challenging the current custody arrangement so that they spend more and more time with your daughter? There is a certain undertone in his remarks that suggests that he thinks he's doing a much better job as a parent, and that he and his wife are grooming your daughter to distrust you and withhold information from you, and that they are ready to take your place at any given moment. I don't say this to cause alarm, but it wouldn't hurt to start documenting these situations in case you have to defend yourself in court in the event that they sue for permanent custody.
In the meantime, I think you need to keep things very matter-of-fact in your communication. Stress that you all have the same goal: positively parenting your daughter. That requires wide open communication between you, her dad and her step-mom. You need to keep in mind that it is in your daughter's best interests to not get caught in a power struggle with her father and step-mom, and your daughter needs to learn that there is solidarity between you and her dad, that your rules are consistent, and that communication flows in both directions. That way she won't be able to play one parent against the other.
Good luck!