It's All About Family (Yandere Moms and Sisters)
Before you were born, your grandpa was the man in your mom's life who always supported her, and was her role model who supported her in everything. He had cancer, so your mom studied medicine to work her way up to becoming a doctor to try and save him. Medical school is where she met her girlfriend, whom she introduced to her dad, too then he became a father figure to her. He was there to help support them as best he could, even to go as ar to help them find a good sperm donor facility, which led to 2 healthy daughters who loved their grandpa. After years of battling cancer, though, it finally caught up to him when it came back, then passed away. This was during the 3rd pregnancy... the pregnancy with you.
They saw a lot of your grandpa with you and wanted to preserve your innocence by controlling many aspects of your life. One day, they start to go too far.
