My mom (Rosalia Marrero) is also from Palos Blancos, Corozal PR. She was born to Rosa Marrero & Ramona Ortiz-Vazquez. They had several children, but they seem to have given up all of their children for 'adoption'. My mom was not legally adopted. She managed to reconnect with her brother years ago, but has never met her sisters. She has 2 full sisters: Maria Esther Marrero 1943 and Juana Marrero born 1944 and probably a few half siblings.
Can you ask your mom if any of this sounds familiar. Perhaps she or someone she knows their whereabouts and/or the family that adopted them.