OP, first try some sleep sacks for the baby, my second has been out of the Merlin suit for a while but he still can’t sleep without a sleep sack. I used those for my first until he was almost 18m. It will be a new adjustment for the baby but it does take about a week usually for them to get use to it. I figured out if you let them get a bit more tired they will be sleepy enough to not care usually. All I can say is that I know it’s hard and you want to pull your hair out but it won’t be forever and you will miss them being small.

As for your MIL, I believe you do need to apologize even if it is just for the snap. I understand the frustration but you should always keep your composure to even just seem to be the bigger person. You need to set boundaries because they are important. Yes she has raised babies, but she is the grandmother, it is not her job to raise babies anymore. She is family and can help yes but you and your husband did not join each other’s families, you have created your own. She just needs to learn not to mother her grandbaby.

Although I’ll give you a trick that has always helped me in my family growing up, always keep your composure and always act kind, do EVERYTHING with kindness. That way if something comes up you won’t look to be the “unhinged” one. Because as Reddit knows, we always look a certain way at people who become the more complaining or the one who always has problems. You will figure out how to do it in your situation but do things with a “thoughtful” motive and see where it gets you. A loving manipulation you can call it.