Contacting full siblings who know nothing about you....

I am facing a dilemma. I am currently 60 years old. I was given up for adoption and then the birth parents married shortly after I was born but gave me up for adoption. Through finding my birth Mother I found out she and my birth Dad had 2 more daughters. After 7 years of marriage my birth Mom divorced birth Dad and she married again and had a son I would say approx. 15-20 years later, To get more on point I will not elaborate on my finding my birth Mom but I did so when I was 25 years old and I saw her in person roughly 20 years later when she got word I was getting documents. She was none to happy that I invaded her life and has kept my birth a secret from 3 of the her 4 siblings, and her current husband as well as her children (who I know the sisters are in their late 50's)! Over the years I got all my paper work collected from Social Services, from the Kansas Children's Service League, plus I met relatives on my birth father's side who knew of my existence, as well as found 3 other 1/2 siblings that my birth Dad had with another woman and who were abandoned by their Mom and put into SRS. As time has gone on I would spend time trying to find the sisters. The birth Mom gave me their first names. Of course I had no idea if they were adopted by her current husband, and/or married. Birth Mom did say she had left the state after divorcing my birth Dad and had not moved back and lived somewhere out east, which I've since located where they live. I finally at the beginning of last year, after many years of searching found the 2 sisters and 1/2 brother on FB. I knew for sure because there were photos of my birth Mom on their page. I couldn't believe it!! I didn't know what to do and talked to my children who are in the middle 30's and they of course encouraged me to contact them, as well as my cousin who was adopted as well and has found her birth family encouraged me as well to contact these siblings since we have are older adults already. I did create a letter to send and had the girls read it and see what they thought but I never had the courage to send it to any of them. All I have thought about it is how upset my birth Mom was that I had found her and has kept her secret all these years and who was I to come and along and open a big can of worms. It could cause a big issue for their relationship with their Mom and vice verse. I didn't know if I could live with that so I gave up on that idea. I turned 60 just this past month and my middle daughter called me this past week and told me she had messaged one of the siblings and told them about me as well as pasted a copy of the letter that I had created a year ago in the message. She said that they deserved to know and they should be old enough after all these years to decide for themselves if they want to meet me or not. I couldn't' believe my daughter did it, but I understand why; we went as a family to make a trip to WA and CA to meet my birth families aunts and families and learn more about them and they have always been apart of this process but it affects them as well. It has left a pit in stomach to know what may or may not happen. This just happened 2 days ago and she hasn't heard back from anyone yet, so we will see. Has anyone else had this experience? How did it play out? I am so scared how the birth Mom will react when she finds out, and I'm nervous that these sisters know little if nothing about their past. In fact, the 1/2 brother may not even know they have different Dads. I would love to hear about other experiences! Thanks!!