The show's new series producer last week announced a string of new signings who will be part of two new clans - the Costellos and the Sharpes.
Speaking to Inside Soap about what else he has in store, Marquess confirmed: "Later in the year, there'll be another family but they're still very much in development.
"They'll arrive with a story about how kids react when their mother is becoming more and more selfish in what she wants, and sort of screwing up the lives of her children in the process."
Meanwhile, on what viewers can expect from the Sharpes, he said: "They're going to utterly change one of the existing character's lives - in a Sliding Doors kind of way. If this character had chosen to go right instead of left, things would have turned out very differently for them."
Marquess joined Hollyoaks in January and is currently steering a period of reinvention at the teen serial.