How old is baby? And pil wants to introduce juice?
Just let them know that fruits are okay if above 6months old. Eg blueberries , Apple, pear, banana etc
100% Fruit Juice will be at 1-2 yo is still acceptable.
Have to introduce slowly n 1 by 1, eg a week or so.
Not all babies accept new food right away.
We are not being too protective but just it takes time for baby to accept new food too.
Maybe you can discuss with PD, ask him/her write a testimonial or any memo. At least have some support. Husband will not argue with you much.
Anyway show your hubby this
http://www.gtgoodtimes.com/2018/03/30/newborn-suffers-indigestion-bleeds-death-grandmother-insisted-feeding-solid-food/
https://sg.theasianparent.com/newborn-baby-food-intake
This grandma said, she use to feed her own children same way. But end up, this is what happened
Rae