On the 7mth old not sleeping throught the night. I can suggest some things that may work. I have a 5 month old weighs 19 pounds, so he loves to eat.
Three things we've done to get him to sleep through the night.
1. Give him a bath each night (bubble) with the lavender bath stuff.
2. Feed him a oatmeal bottle (extra think), or feed him an 8oz. bottle of formula.
3. We put a humidifer (cool Mist) in his room. It clear the air and makes it easier for them to breathe.
I hope this helps.
The matter on the mother in law issue. Well i do understand. My mother in law is awful too and my husbabd and I fight about her too. All you can do is tell your husband that your his wife and mother of your child, he should stick to your side.
If you can not slove this with your husband then go to the source of your promblem, being the mother in law. Tell her what she is doing and make her aware that this does not help matters. She may not relieze what she is doing to you two.
I hope this helps. I wish you the best of luck.
L.