The other birth mom

I am the second girl to place with my birth daughter's family. When my baby was born, it was really hard on her older brother's birth mom for awhile. We hadn't met yet, and she was scared that I was going to hurt her relationship with the adoptive parents. For a time, since I had placed a new baby with them, I was in the spotlight and she felt pushed aside. Since I met her, our relationship has been amazing. She's realized that I'm not here to hog all the attention, and our personalities just click. I'm so grateful to have her in my life because she's the only other person who knows exactly what I'm going through. We tell each other everything, and I consider her my sister. We text regularly and I see her as often as I can. Now our adoptive couple is looking to adopt again. We're excited for them but scared for us. We have heard and seen so many stories of another birth mom coming in and not getting along with the other birth mother(s) and causing issues. We feel like it's a blessing and a miracle that we get along so well and that we can share rather than compete. We don't want that balance to be thrown off. For now, we're just trying not to psych ourselves out, but we are nervous. What can we do to ease this worry, and prepare for whatever happens?