Night sleep problems

Hi everyone, I wanted to ask advice on controlled crying or any other way to put my boys to sleep without me being in the room for more than an hour.
I have a 2 year old that was great at going to sleep on his own. & a baby that did the same as soon as I put him down in the bassinet. Ever since the the 9 month old went into the cot which is in the same room as the 2 year old, it's all gone down hill. I've done it before with the older one, I read save my sleep and it worked so good. But now with the younger one it's hard, I can't leave him in there crying as they sleep in the same room. They both start screaming and crying as soon as I walk out. The younger one just stands up in the cot screaming, I've left him for 45 min once & he was still standing when I went back in. So I can't do that anymore. It breaks my heart. Any advice would be appreciated. Thank you