Hi and welcome !!! I am sure you will find as I do it's nice to chat with people who really understand !!! My advice and practise is to have each child under 3 in a playpen , I put them in a darkened room ( right now everyone has their own space ) and I give a cuddle and lay them down and walk out . I do believe in CIO , but I will check every 20 min to lay them back down if they are standing up crying . I do not speak , just lay them down and leave the room .
The first day is a test , lol I just make sure I have the new child farthest away or start them to nap approx 1/2 hr before the rest to see how it goes .
I have an 18 month old dck and the first day she climbed out screaming and it took us almost 35 min of me putting her back in without speaking before she slept !! Now she will cry but doesn't bother getting up !!
I like the fans and white noise idea !!! I would def try that if I had one who wouldn't settle !! The information learnt here is awesome !!! I am mom to 5 and I have really benefitted from the advice I have been given here myself !!!!!!