Responsável is common for both genders, and adjectives have to agree with the subject in gender and number. Words that end -vel, changes into -veis in the plural. Responsável (singular), responsáveis (plural), alike Incrível (incredible), incríveis.
In English, responsible can mean both being liable for (They are not responsible (for the safety of the kids over there).) and being reliable (They are not responsible. I wouldn't trust them.) Is this true of responsavel?