Napping while being held

My daughter is 18 months old. My in laws watch her 2-3 days a week. I’ve asked them in the past to put my daughter down while she naps, but they constantly defy my request and they send me pictures of her sleeping on their chest on a regular basis. I feel like recently my daughter refuses to stay asleep unless she’s being held and I’m wondering if my in laws are to blame for that... anyone else have a small child that has attachment issues during nap time? What are some things you do to break that habit?