The Harloc Mirror by Vincent Vurchio

An ancient portal to a nightmare universe, long ago thought lost, is uncovered by a family seeking to escape the hell that big-city life has become. When two members of that family become trapped inside the Harloc Mirror, a trio of supernatural investigators must follow them into their worst nightmares and hope to discover a way back again. Success depends on their courage, ingenuity, and willingness to sacrifice old secrets that could prove as destructive as the Harloc Mirror.