Is it possible to grand Child Custody to three or more different people? I am a 19 year old mother in school.

You should consult an experienced family law attorney to discuss your options under the laws and procedures governing the award and transfer of child custody in your state.   I presume from the way your question is written that you already possess a family court order awarding you sole custody rights.  If not, that has to be your first step before you can assign your parental powers to a third party.  The attorney can assist you in trying to negotiate a voluntary custody agreement with your ex-boyfriend; if that fails, s/he can seek a custody order from the family court that awards joint custody to you, your mother and your friend.

But, please note that if the family court transfers custody to your mother and/or friend, you are not guaranteed to have input into decisions about your child.  If you just want schools, doctors, hospitals, banks, etc. to know that your mother and/or friend has authority to make decisions and serve in the capacity of a parent in the event of an emergency you are at school, you can accomplish that without a court-ordered transfer of custody.  A family law attorney can help you identify all of the institutions and individuals you would need to contact, and prepare any necessary documents.