Complex sentence: The female branch are the Franciscan Sisters of the Immaculate; the last branch of the family is the Franciscan Tertiaries of the Immaculate, which is composed mainly of lay people.
Split into simpler sentences: The female branch are the Franciscan Sisters of the Immaculate. And the last branch of the family is the Franciscan Tertiaries of the Immaculate composed mainly of lay people.