in law advice needed

so I have a unique set if in laws, and to break it down, with our first baby my husband's family told his ex wife and my step kids before we could/were ready to, we've recently told them baby #2 is on the way, and we will be joining them for christmas and will be taking my step kids, I need a way to tell them not to say anything about the little bean in front of the kids or his ex wife, because clearly it will go better for everyone if it comes from my husband and I, I don't want to sound rude, but I feel the need to be stern so they know I was/am not happy about it happening once before.