CARBONDALE — Pravin Varughese was 19, a criminal justice major from suburban Chicago. Molly Marie Young was 21, an aspiring photographer from Marion. They never met while studying at Southern Illinois University, but after their unresolved deaths, their grieving families have joined together to press for answers. Last week, the families’ campaign led the local state’s attorney to step down in favor of a special prosecutor in the Varughese case, as he did earlier with Young, amid questions about …