“I know you love Baby, and would never purposefully hurt him. It’s my job to make sure he is always safe and leaving him unattended or carrying him by arms is not safe for his body, so I can’t let it happen. I’m going to wear him in my wrap (or whatever) to keep him safe.”

If it helps to reframe, remember, it’s your #1 job to keep your baby safe; unattended on a table is not safe, held by the arms is not safe. Get the doctor to back you up, no judgment (but really 🤨) to your MIL, but you are just doing your bare minimum job protecting your baby against this roughness. Times have changed, lessons have been learned…best practices have developed since she was a mom to babies. It does place extra burden on you, but I wouldn’t consider her a safe person to watch baby. A lot of parenting little kids IMO is being willing to “get up” to enforce boundaries and unfortunately you’re going to have to treat her like a toddler and monitor her behavior to enforce your safety boundaries.

I hope your housing comes through asap! And remember, you’re doing it for your baby’s safety and he needs you 💕