Sharing Icloud Photos

My whole family in my household is on the same icloud account and our phone photos merge sometimes from time to time. We never could figure out to get that to stop. However… Today, I looked on my photos to find something and I noticed I only had 3,000 photos Total. When I had almost 17,000 previously. I also noticed I had some of my sisters most recent pics that she had taken merged again. So I decided to look at her phone. I found that she also has some of my recent pictures as well. My sister is not missing any of her original pictures (like me). But she does have photo albums that I created on my phone that are on hers as well. Where did my 13,000 photos go ?? And How can I get them back?? Tia