I second what @Ell said. Get on the same page with your partner and talk about how you’re feeling (which is 10000% valid btw.)
Hands in the mouth at this age is developmentally appropriate and completely normal. If she can't respect your boundaries on feeding then she is dangerous to be around your child. I can imagine she would be feeding baby inappropriate foods such as whole grapes when time comes. Discuss how she makes you feel with your partner and bring evidence backed research with you. Hopefully he can warn her that unless she falls in line then she will not have contact with bub.
If they aren't listening to you his mother then stop seeing them. Simple as that, you need to put your foot down. I would have kicked off with her giving cream and custard. I had to and I still do 3.5yrs later
Unless you rely on them to babysit, I would stop contact until they improve their actions. This is all not only disrespectful but super dangerous.
oh heckkkk no. they wouldn’t be seeing my baby if they didn’t respect my boundaries. giving sugar to a 3 month old is insane! i’d be livid. also the hands in the mouth is so normal and actually something that is supposed to happen at that age, they’re exploring their mouth and also using their mouth to investigate objects etc. it won’t create a bad habit because it literally goes away.. that only lasted for a month for my baby
Stop contact if they’re not respecting boundaries.