I am going to tell you a little about my expirience, in as little words as possible. I hope!
I am the product of divorce, and when my mom had her second baby (7 years younger then me) was born I had some of the same issues, My mom did try to involve me in the day to day of the baby and that was a good thing, but I still had a hard time with situation and would constantly pull the " I want to live with daddy, you don't love me ect,." and my mom would ignore me or say that wasn't possible ect,. and then one day she had enough and was tired of hearing I want to live with daddy, she looked me right in the eye and said and I quote "your wish has been granted" walked in my room and packed my clothes, nothing else in the room could go, put me in the car and started drivivng, I can remember sitting there thinking this isn't happening, about ten minutes into the drive I was so upset at the fact she was actually taking me, I started begging to go home, 5 minutes later we were on our way home, and I never said those words to here again.
Fast forward to my own kids, my husband and I have been married for 17 years but five of those years we were seperated, and he had a couple of kids during this period, and very little contact w/ our 2 children, but that didn't stop the " I want to live with daddy" when things weren't going thier way, and your right it HURTS to hear those words, and then one day like my mom, I was sick of hearing it, they were 3&4 at the time, and I did exactly what my mom did, only thier clothes, and told them how much I loved them and would miss them and how sorry I was that they didn't love being with me as much as I loved being with them, and started driving, luckily a few minutes in they changed thier mind, And I say luckily because I had no clue where thier dad was, he only called us occasionaly.
Will this work in your situation who knows? But it is a thought, also the age of 4 is a trying time already, sometimes the most easy going infant/toddler can become really difficult around this age, some of it, I think is the fact that they are capable(sp) of doing so much but as parents we start putting down stronger boundries and things become a little less "carefree". I would say be patient,and don't acknowledge the bad. And one thing I think one of the other mothers mentioned is making time only for her in the evenings, not just the weekends, that is a long time to a 4 year old, the equvilant of a month for us.
I am raising my "step"-children, have been sisnce they were very little, and are mine in every sence of the word, but for the first few years I did very little of the "punishing" that was my husbands job, I did discuss what I wanted to see be done with him but the actuall punishing was done by him, and when he wasn't home I would use a chart to show what behaviors they had that day, and not just the bad but the good also, and then I would let them know what would be discussed with thier dad when he got home, obviously he couldn't use time outs for the actions that happened when he wasn't home, so we did things like take t.v time or removed a toy from thier rooms ect,. I am lucky today they see as thier mom and we are a large family 7 kids in total our older 2 his 2 and then our younger 3, and have no issues correcting them today, but it is a process, and I see that you and your husband have been togather for most of Hannah's life but he may need to pull back just a little and give you and Hannah some time to work through this, and maybe instead of focusing on Hannah, become that much more involved in Aubree, so that you have the spare time to help Hannah get through this transition, I don't know if that helped any, but I will say good luck!