Firstly, I agree, it WILL get better. But I also agree,not right away. Iknow it's hard to hear now, but as soon as you know it babe will be 18 month go and you'll have weathered the really emotionally hard stuff. We never had any issues with jealousy or feeling bad but I know I was sooooo nervous about it. Also know, emotionally you are in a hard spot right now. I know I have quite a bit of emotions swirling around the first two weeks. Nothing seems right and everything seems strange, different, just not the same. Mild PPD? maybe. But even if it's not, you are still a hormonal mess so don't be hard on yourself.
When I say it will take a while, my issue with my 2nd was bonding. It took 10 months for me to feel close to her. Her older sister was my first and I literally thought I ruined her life at first by having another. However fast forward 3 years and I'm listening to the two of them, along with their baby brother, giggle and laugh and whoop it up in the playroom. So give the issues you are dealing with right after birth time, give yourself time and try and do as many things as you can with them.
I took a different route and didn't single any of my little ones out to have special time. We had to function as a team so IMO, I had to let them know it was fun to be with each other, regardless of what stage each one was going through. both times I had a new baby, my other 2 year old was hitting the tantrum stage, so it was tough. But my mindset was kind of like we all have to get through this together and help each other out. We are in this together so singling one out in my experience didn't work for us. And it seemed to work for us because we have never had any issues with jealousy. My kids are extremely close and are used to doing things together. Even to the start of Kindergarten this year for my oldest. My 3 yo took care of my 12 mo while I was consoling and encouraging my Kindergartener for school. I have to count on them for help, they all know that and expect that they might have to just tag along when we do for another, but then the others will reciprocate. Sooo.. all that to say, what worked for me was including them in diapering, holding, excessive praise to build their self esteem, showing them pictures of them doing the same things when they were babies etc. There were plenty of times in those early months where i would be sitting in the rocker with 4 dollhouses on my lap while I was nursing the baby. I could hardly stand it space wise, but it's what needed to be done so I wasn't off alone nursing. And my middle dd had to nurse every 90 minutes until she was 10 months old. I would literally put her down after nursing, go in the kitchen for a good cry and them come out and play with them. That reminds me, I always kept them in a close proximity to each other. If older dd was laying on the floor playing or watching tv, I would put baby on a blanket right next to her so they both could benefit from the closeness. In a larger family, you simply don't get space here!

. Learn it now!
How you handle this from the beginning will believe it or not affect how they relate when they are older (sorry, no pressure i know!). so you have to find which style works for you, try it for a week and see. If separating as soon as possible and giving them special time with mom works best then do that. If involving them more, nursing on their ground even if it's uncomfortable and pushing closeness and teamwork work then do that. Every temperment is different. I would also say those early days have helped me relate to each of my kids in a different but similarly loving way. Each gets the same amount, I feel evenly spread, but in a much much different way. I never thought I could do that.
Give yourself time mamma. Have your dd grab a few diapers and wipes for you, clean up spit up, whatever makes her feel good. Make sure your responding to her in your body movements and it will get better. Also maybe a few new toys that would be equally interesting for your oldest and middle will help them get back in thier groove.
hugs and good luck!