New 8 Week Old Kitten, Older Cat

Hi everyone! I am new to TDK and was hoping to get some feedback on a few things regarding a new little bundle I brought home. Please forgive my long post. I have literally never posted anything on an online forum, and I’m very worried about handling this correctly, so I wanted to be thorough. So please share your thoughts with me! First, let me give you some background info.
I already have a 1 year old cat, my “Sweetie Pie”, who is super loving and affectionate. I got her at around 2-3 weeks old. Her mother was hit by a car and passed away, and my Sweetie Pie was the last of the litter, but no one wanted her (my guess is bc she was so vocal, hahaha, but I loved it!). In any case, I happily took her in, bottle-fed her, litter box trained her, the works. I have a feeling she thinks I’m her mom. She’s absolutely a wonderful part of my life.
After getting her, I learned that cats prefer to have a buddy, as they can get lonely. My roommate ended up having a cat for a little bit of time, while my Sweetie Pie was 5mos – 9mos old. The introductions took about a week, but after that my Sweetie Pie loved the new cat. They were constantly around each other, playing, cleaning each other, sleeping together. Unfortunately, my roommate had to give hers back due to her own circumstances. This left my Sweetie Pie without a playmate until now.

I just got an 8 week old kitten to be her playmate. She’s the “Little Baby” who was the runt of her litter. The owners told me she was handled every day, but she was definitely scared when she realized a stranger was holding her. Still, she allowed me to hold her the whole car ride home, while I spoke softly to her & hummed (same ritual as with my Sweetie Pie), and she actually began to fall asleep, which I thought was I good sign. However, every time she realizes how high she is in my arms, or if I walk around, she gets scared & meows, little claws clinging for dear life. Now, I for sure expected a new kitten to be scared, but I am not used to handling one that is. My Sweetie Pie was so young when I got her, that all she wanted was to be held and carried around. She never developed fear of me and always wants to be around me and other people. So I am trying to adapt to the Little Baby and want to make her as comfortable as possible. I want to do whatever I can to make her feel safe and want her fear of me to subside.
I had my friend hide the Little Baby when I first brought her home, and I greeted my Sweetie Pie as normal, but she smelled the Little Baby on me for sure, and became a little cold with me. I left the Little Baby on my bed for a while so she could get used to my area, and I felt bad bc my Sweetie Pie is definitely used to going in & out of my room as she pleases and she didn’t like that I kept her locked out (again, she knew something was up). Therefore, I kept talking to her lovingly (ignoring her slightly dirty looks that made me feel so guilty), and took time to play with her for a while as we normally do. After that tired her out, I put her in another room, and then went into my room to spend time with the Little Baby. I spoke softly to her while she was on my bed. I’d hum, rub my face against her, and she allowed me to do it and fell asleep. I tried putting her in a large box I set up for her in my room to sleep for the night, but she meowed when she was in there. So I put her back on my bed, and she slept next to me all night. She kneaded the blanket and purred once or twice, which was a good sign. But the next morning, she backed away whenever she saw my hand coming to her slowly, as if she didn’t want me to touch her.

My concerns are: how do I get the Little Baby to feel safe, to enjoy being held a good amount every day, and to enjoy receiving affection from me/others? Also, my house was relatively quiet her first night here, but we do not consider ourselves a “quiet” house most of the time. I play loud music every day, we have TV’s on, we speak loudly, laugh a lot, sometimes we have people over. I kept it quiet the first night to help reduce her fear and shyness, but at the same time, I don’t want her to get scared once we continue our normal routine at home.
My other concern is with my Sweetie Pie. I do not want her to feel upset to the point where she’s not as affectionate with me. Her coldness that first night hurt my feelings. I ask myself, “is she slowly going to begin to reject me?” She hasn’t seen the Little Baby yet, so she hasn’t seen me be affectionate with her. How do I make sure to maintain the same type of closeness with my Sweetie Pie? Eventually, there is a point where she will see me with the Little Baby, and I am very afraid that my Sweetie Pie will change her ways with me.

Please share your thoughts with me. Have any of you had similar experiences? I want to handle this as best as possible, without losing out on either one’s love & affection, but also having them become like sisters.
Thank you, much appreciated!