People lose all common sense with tiny babies, and I’m not talking about their parents.
Newborns are not born with some super-immunity pack thanks to the placenta and breast milk; their ability to fight illnesses their mother hasn’t built immunity to is weak and they can deteriorate terrifyingly quickly without some of the external indicators present in older children and adults with with the same illness. Some illnesses that are unpleasant for adults can kill newborns. Even milder colds can blight the early weeks, one of DH’s barrister colleagues brought her children to see DD1 at a week old, they were full of cold and I only knew when I heard the youngest’s congested breathing as he loomed in close, touching her face. A few days later she had it and was never in danger, but she went from a contented feeder to distressed and battling for breath, and breastfeeds were awful for over two weeks. It was hellish and nothing like as bad as ending up in hospital with a newborn.
The most important bond a newborn needs is with one primary consistent caregiver, almost always the mother. They need that person’s smell and the security that comes with that person materialising and holding them close when they cry. I was luckily able to bf DD1 (expressed for DD2) but I feel sorry for FF feeding mums with selfish family and friends who clamour to feed the newborn, of course they love it because it’s the time when they tend to be most settled and gaze intently into the eyes of the person feeding them… - it’s intensely bonding, but both mother and baby need most feeds to be between them for just that reason! Bonding with wider family comes later when babies are more robust, social, and interactive. A newborn gets nothing out of being held by Uncle Josh. I don’t mean only the mother should ever hold newborns, but I’d never visit and expect a hold and I have had happy visits where I haven’t because the baby has been asleep through the short visit. I’d always wait for the mum to say “Do you want a hold?” if the baby is awake.
I’m always shocked at the vengeful “They’ll be sorry when nobody’s interested when the baby’s 18 months.” I can’t imagine that someone who doesn’t form a relationship with their grandchildren or nieces and nephews because they weren’t given free rein with them as newborns is someone very nice. Loads of people don’t live near wider family but still have loving relationships with grandchildren etc. despite not giving them bottles or even seeing them in early infancy. I’m glad my Newcastle grandma wasn’t like that!
It sounds like this SIL has had a difficult birth and is still sore mobilising 3 weeks on. She must be feeling incredibly vulnerable sometimes needing/ wanting her own baby passing to her or changed instead up just being able to do it herself without significant pain, particularly in front of people she doesn’t feel comfortable wincing, hobbling and huffing in front of.
I agree a sign is ridiculous but only in a way that reflects badly on the parents if they have family and friends who would never kiss a baby on it’s face or come with colds or pick up a sleeping or settled baby. It seems like this baby’s parents don’t have that confidence and “using your words” as everyone always suggests, doesn’t always go down very well and can be very difficult to do with pushy people, particularly if you are sore, exhausted and hormonal.