Hi!

One problem is that he shares a room with Louis so as soon as he cries out I jump up and go into him so I don't know if he's just used to me resettling him or giving him the dummy to get back to sleep. I can't let him even grizzle for a minute to see if he'll go back to sleep on his own because I'm scared Louis will wake up...
This bit caught my attention

I was exactly the same with my DS from when he was born - I jumped out of bed at the first peep so he wouldn't wake our two year old up. By the time DS was 4 months old we were having sleep issues and things really slid downhill between 4-8 months, he just totally lost all ability to self-settle. He was so used to me appearing with a boob out to keep him quiet, that by the time he was 8 months old he was waking hourly and would NOT go back to sleep without it. It was horrible, I was a mess.

Someone suggested to me that my DD would probably sleep through a bit more noise than I gave her credit for so we tried it. We never let him scream, I don't use CIO but I did allow him to whinge and whine a bit as he resettled and we found that he would do that for maybe 5 minutes and go back to sleep. On the rare occasions he did get wound up and start bellowing DD did sleep through it, she never even stirred. That really surprised us.

It's hard when you're trying to avoid waking another child and the natural reaction is to do what you're doing, but yeah I definitely found it set up more problems down the track