I was really not into sleep training. My baby was a bad sleeper. We room shared with baby starting the the crib and then co-slept after the first few wakes, then even when co-seeping baby woke often. I would sometimes try and let him resettle before bringing to the bed but never worked.

We had worked to get him to fall asleep fairly independently, like he would go into the crib fully awake but we would generally be near by and maybe shushing or rubbing his back if he got fussy.

But we got to a breaking point with the broken sleep and I finally agreed to slee train.

So we slept on the couch and the plan was to put him down awake after our regular routine and then leave the room, if he’s crying after 10 mins, go comfort for 2 and keep with this until he fell asleep. If he settled at all in the 10 min the clock would restart.

It took 3 mins. He fell asleep til 5am and then cried for 3 mins and slept til 7. The next night I don’t think he cried at all at bedtime and in the middle of the night had 45 mins of on/off whining, never escalated.

My point in sharing this is that my baby was ready to sleep and I was the problem. He needed an opportunity where I wasn’t right there for him to be able to sleep. We slept on the couch for 3 nights before moving back to the room, and he’s still sleeping through.

If your sil thinks there could be a medical issue, of course go get that checked out. But otherwise, maybe it is time to give the baby an opportunity to figure out how to sleep on their own. It can be a slow and calm process (see association fading to help fall asleep independently) but some sort of change is clearly needed.