Keys decommitted from Penn State the day James Franklin was fired.
Brown is the No. 2 player in Pennsylvania.
The Nittany Lions will welcome the Cornhuskers back to Beaver Stadium for the first time since 2017.
"These are my kids, and there's nothing more than to make your kids happy."
Allen is 138 yards shy of being Penn State's all-time leading rusher.
Dennis-Sutton had two sacks and tied Penn State's single-season blocked punts record to help break Penn State's losing streak.