It's so hard sometimes isn't it? You really need some good sleep you poor love.

I don't know if I can be much help. I completely understand the frustration of one sibling waking up the other! In the early days with DS2, DS1 decided to start waking up at the crack of dawn, make noise and wake his little brother up. We also bought block out blinds LOL! Luckily that phase passed on it's own.

In regards to your bub hitting his head at the top of the cot, I can only give bad advice . My DS2 would do this too and in the end I used a cot bumper and I would position him at the top of the cot when I put him to bed. I found if I put him at the bottom of the cot (as recommended), he would work his way to the top anyway which would wake him up once he hit his head at the top. Using a bumper and changing his position made a big difference and he stopped waking up because of bumping his head. I feel bad offering that as advice as it goes against the SIDS recommendations!

Waking frequently overnight at 4 months is very common. They get more distracted during feeds during the day and they don't feed as much and are therefore still hungry at night. They seem to feed better and longer at night because there are no distractions. Is it possible for you to feed him in a dark, quiet room during the day? I know this will be hard with a 3.5 year old in the house too.

Also, good day sleep helps achieve good night sleep. Your bub sounds like a 40 minute cat-napper, just like mine were! Babies sleep in cycles (usually 40 minute cycles for some weird reason) and when they reach the end of the first cycle, they don't know how to fall back into a deep sleep. A trick I learned with DS2 was to sneek into his room just before the 40 minute cycle was up. I'd watch him and as soon as he stirred (he used to sigh and move his head), I would pat his tummy. He would then sometimes go back into a deep sleep. This would work on average for one of his three naps a day. I kept persevering and before too long he got the hang of resettling himself.

With DS1, we invested in an Amby baby hammock and would bounce him back off to sleep when he woke from his 40 minute cycle. This worked wonders for him and he eventually worked out how to do it himself too. I highly recommend trying a baby hammock! It changed our lives with DS1. You can hire them if you wanted to try one out.

Both boys ended up becoming excellent sleepers after a lot of persistance.

If you are really struggling, you could try book into a sleep school who can teach you some settling techniques.

Anyway, sorry for the long ramble, I was just trying to think of all the things I tried that worked for me!

I really hope you get some good sleep soon .