baby fell, started to being fussy and vomitting

Hey mom... I want to share. Yesterday, my 7-month-old baby fell because of my 4-year-old niece. She insisted on carrying him even though I told her not to, but her mother (my sister-in-law) always says, "Just let it be... they love each other like cousins..." And true enough, they both fell. My baby hit his head and cried really hard. He was so fussy... and shortly after, he vomited. I immediately wanted to take him to the doctor, but my sister-in-law said, "You're being overly dramatic." But I don't care, mom. My child needs help. I don't want to take risks just because they are related. At the hospital, they checked him thoroughly and observed him... thankfully, everything is okay. But I still want to know how I can live far away from my husband's family.