MIL disrespecting me

My son is 3 years old, and when he is at my mother in law’s house, they still give him bottles of baby milk. I told them I have been trying really hard to get him off of bottles and on to sippy cups, so I asked them to please stop giving him bottles. They still do it. Even right in front of me. My son was crying over a toy and they were like “aww you need a baba milk”? I was like “no, he really doesn’t, Please don’t give him one.” And they told me they were giving it to him anyway, and if I didn’t like it I could go stand outside. This is a constant thing, they never respect my wishes. Worst of all, my husband just stands there and laughs. What should I do about this? What would you do?