Your MIL will survive. It's just a couple of sleep interrupted nights.
So nice of her to help you. Just warn her ahead of time that he is waking
up during the nigh to feed.
That way she'L. be prepared & she will know to definitely feed him!
The go through stages and spurts.
He may be growing, teething or both.
Try some Baby Anbesol to rub on his gums.
Make sure she has Infant Tylenol if she thinks his pain is keeping him up.
Make sure to SHOW her the approp dosage.
He could just be hungry so I would get up as you are doing and feed him.
Girls sleep through the night sooner than boys in my experience.
Happened w/my friends' kids, too.
No, I would not let him cry it out. It's his only way of telling you he needs something and he sound hungry. So just do what you are doing and feeding him at night when he wakes up and cries.
My son did not sleep longer than 3 hrs at a time for awhile. He, also, did not sleep through the night for a LONG time. I just went along with it rather than trying to fight it so we'd all get better sleep. We got through that long phase fairly easily. Looking back, I'm glad I did it that way. I rested whenever I could.