I know this is not what you are looking for but I wanted to put in my 2cents.
I have 4 kids and btdt in tears frustrated with bedtime very pregnant and thinking things need to change because I can't handle this with a newborn. Similar age gap to your Los.
I actually found what helped the most was me changing my view on what needed to happen and what I thought I should be able to expect from them. It greatly decreased my frustration and stress level.
Before our last baby arrived I thought that I should be getting Ds2 to fall asleep on his own at night instead of nursing to sleep. Everyone agreed how much easier it would be if we could get to do that.
I started sitting in his bed and trying to get him to sleep. It took me about a week of tears and frustration for both of us for me to realize that what we had done all along didn't need to change because of the baby. We went back to nursing to sleep. Most nights I nurse them both to sleep in bed and everyone is happy.
18 mos is still really little in the scheme of things even though they seem so big sometimes.
My advice is do whatever you need to do to make everyone happy and able to sleep.
Try not to stress about when the baby comes.
I know easier said than done but things will eventually become routine with 2.