Hi there. Our youngest 2 still share a room, although I am contemplating giving up our spare room so they can have their own, especially since it's a boy/girl situation. Our son was 4 when our youngest was born. We live in an older 2 story house w/ bedrooms upstairs but 1 on the main floor. We used a portable crib (w/ wheels) and E. actually slept in our room for a little while, and then the living room until she was ?about 6 months old--we would put her down in our room and wheel her out when we were ready for bed. We then moved upstairs to our spare room, when she moved upstairs to our son's room, so we could be on the same level until she was older. She's 2-1/2 now.
There really is no perfect solution. I agree w/ the some crying approach. I think that learning to settle yourself is an important skill, and pays off down the road. On the nights she didn't settle right away, we used to let her cry a little, go in after a little while if there seemed to be no end in sight, and comfort, but not pick her up. Usually after a few times, she was ready to sleep.
You can also work on this at nap times, when, hopefully, your older child is not in the same room. And hopefully bedtime will go smoother if she is learning to settle herself well at nap time. Try to put her down when she is drowsy but not already asleep from nursing/bottle, at least some of the time. Although it is blissful to have them fall asleep in your arms and just hold them a while.
It's just tough, especially on those nights your husband is away. Just keep working towards a long term goal, and try not to get discouraged with the short-term ups and downs, as with any goals you have for your kids. If you can settle the baby in a portable crib or playpen in your room, so that your older child can get settled on her own, and later move the baby, that might work, at least until baby gets better at going to sleep on her own, more consistently.
My son fortunately learned to go to sleep regardless of what E. was doing. Sometimes before the baby, depending on how the schedule was going. But every child has a different temperament and needs. He has had to give up a little w/ sharing his room. We take an afternoon quiet time, and often his had to happen in another area of the house. It has been tricky to teach him about making his bed 1st thing in the morning, because we sneak him out in the morning to get dressed for school. She gets into his stuff sometimes. And I have not had the energy to train her to be alone in the room and stay out of his stuff, so we just don't leave her unattended in their room.
The upside is that they learn more about sharing space and considering others. It works on some of the selfishness so prevalent in us all.
Hope this helps. Be encouraged. You are pouring your life into these precious kids and it is a most worthwhile endeavor.