Hi C.,
When I read your post, I thought I was reading about myself! I too, have two small kiddos right in line with the ages of yours. Our two yougest are 20 months and 14 weeks, so we have the baby in our room and a monitor for our toddler, whose room is upstairs. We've experienced, like many others I'm sure, the painful "wake in the night" process, and fumbled our way thru what worked best, what helped, what was tolerable, what was a disaster. While there's no "one size fits all" answer, we knew our daugther is quite headstrong and so unfortunately we had to suffer thru a few nights of crying it out (all of us, I might add!). What would always get me thru these hardest nights was knowing that no matter what, the next morning she would wake with such a blazing happy smile, ready to greet me with a hug, and all was forgiven. And in the end, we made it thru and now have semi-normal nights and mornings -- a huge improvement, for sure.
I agree with Kari that the darkened room may definitely help. You may also consider using "overnight" diapers -- which are usually a bit thicker and seemed to help with my daughter (her normal diapers weighed a ton when she woke up).
In addition, we have a video monitor on our toddler. She went thru the phase (and still does during random times of the night) where she just cries out in an effort to get us to come in her room. Sometimes it's for just a few minutes and other times it drags on until she gives up. For some children you can go in the room, console them and then leave the room again, but in our case, that just seemed to make her even more angry if we went in and then left again. So, that wouldn't work for us, but we hated that we had no way of confirming that she was truly ok. With the video monitor, we are able to see her and know that she is fine, and we can also tell if she is sitting up, standing in her bed, etc. Sometimes she sounds so insistent, but we look at her and see she is actually laying down, and we've learned when she does that, she'll fall back to sleep within 10 minutes or so. She also does this in the morning, when she wakes too early. This may help your husband a lot to just watch her, know she is ok without having to go to her, and see that she falls asleep. When he leaves, he can bring the monitor to you, where you can continue to keep an eye on her while you are resting and she sleeps, without having to go back and forth (and back and forth) to her room.
I hope these suggestions help a bit. Our video monitor is beyond great -- we have the kind that are hand-held size -- and it has helped tremendously during the painful bedtime and morning "cryouts".
Best of luck to you!