Sorry for what you guys are going through.
Shuke, I know exactly what you mean re your MIL. My mother is famous for stuff like that. When she found out that my brother and his wife were having trouble having a second child (apparently their first was something of a miracle), she told him that his wife shouldn't have taken any meds for post partem depression, and she should now take more vitamins. Completely dismissed all the different doctors' advice. For my sleep apnea, she keeps asking me why don't I try going to sleep an hour earlier, in a tone that suggests this is the simplest thing ever to fix.
Yeah, I have a very opinionated mother too and she was furious with us for not forcing our daughter to sleep in a crib with a fixed bed-time. She made sure to tell us this at every opportunity and was very critical anytime she came over to babysit (which was very infrequent). And while I see her point, I also see what kind of child we have on our hands on a daily basis and know that forcing a strong willed, very active, very vocal and very head strong child to sleep in a boxed jail cell when she wants and succeeds at sleeping in our bed is and was a futile exercise. Finally, it came to a head last month in an argument with my mom completely unrelated to this crib/sleep issue...she brings it up and just hammers us. I finally said "Look, I have more kids than you. I do not need nor want your parenting advice, especially considering 50% of your children
are feckless, selfish, financially and morally bankrupt and the other 50% is my sister. My sons are well mannered, well behaved, young men who excel in school and collecting friends so please, no tips from you needed. We got this."
Then I dismantled the crib and put it in the garage and am shopping for a toddler bed at garage sales.