If your mom friend or dad friend posts a cute pic of their baby to share with you please do not comment on their parenting choices. Unless there is possible danger, and or your just giving friendly advice, you come off as a dick.
I’m sorry for being so blunt, but I fear you won’t get the point if I don’t.
For example, if your friend posts a pic of her two month old do NOT comment “why is that pacifire in her mouth”- just because you are anti-pacifire doesn’t make your parenting choices the only choice.
This is totally different if they’re expressing frustration for something and you are providing suggestions. Its also totally different if you see a potential hazard.
That being said if your fellow mom/dad is co-sleeping don’t degrade them for the choice. You can ask if they have considered all of the risks(you may even provide the risks) but know over all it is their choice. Do not say “Don’t let that baby sleep in your bed!”- thats just rude.
Know the difference between advice and a command. Do NOT command other people on how to take care of their child. Its frankly just makes you look bad.