The parent section of the AMCAS is optional and you could list just your mother given that your father was "not in the picture".
You say you were "at school". That is a strange phrase; in the US we usually say "in school" unless one was in boarding school.
Did your situation as a kid put you at a disadvantage in going to college and continuing with your education? That is what AMCAS is getting at.
You might want to be careful about disclosing the wife & 1.5 kids ... it could raise unspoken questions about your ability to handle medical school in addition to your other responsibilities.