Just chiming in to say you are not alone. My friend was telling me the same story about her in-laws. We also had a similar experience personally where we had to tell my mother-in-law that we will not be receiving her if she shows up at our house when she claimed she will be driving here from several states away.

Anyway, I have a newborn now and you can imagine the terror when my older child came down with a dry cough the same day we brought the baby home. We had been strictly isolating but had no choice but to send the older one to a babysitter while we were in the hospital, and she must have picked it up there. The could-be-Covid-cold circulated around our house and I ended up taking the baby into urgent care with cold symptoms. The congestion turned out to be just from reflux thankfully, but the point is that having any infectious disease in the house with a newborn around is alarming even under normal circumstances, but with Covid going around any sign of sickness is horrifying and I would not wish that fear on any new mother. Hold your ground and establish boundaries now or this will just be the beginning of a long battle.