Sleeping help

Need help/ tips desperately. Long story so thank you for reading

I have a 18mo and at 2 months she started sleeping great at 4 months I went back to work and her solid sleep went to shit so my husband and I needed sleep for work and started sleeping with her it was a temp solution at first but she wouldn’t sleep without us. So we figured we’d move her crib right on our bed to make an extension in a way and it worked perfect.

Then as she got older I got scared to move her to her own room , her room would be in front of the house to the right while we’re in back of the house to the left 😬

Then I got pregnant and baby was born , now me and my husband are sleeping in separate rooms. Me with the newborn (breastfeeding) and him with the 18mo. The reason we did it is they would wake each other up and then no one was getting sleep.

I feel it’s my fault because I was attached to my 18mo and she was sleeping so great on her own / with us .

We’re going on week 3 of this and can’t do it longer I need my husband and bed.

How can I get my 18month old used to her own crib and room ?! How long can I let her cry for ? I’ve bought cameras already so that I can watch her