With Cedric Morgan's interference, Ronan couldn't possibly ignore his proposition of firing those men. In fact, Cedric's suggestion helped him save his face as CEO since he would appear like he supported Marceline's decision just because of Cedric's presence, not because Marceline said so.
If Cedric didn't arrive, the end result would be the same. Even if he would object to Marceline's demand, he knew that he could no longer stop her from firing those men.
The Chairman pampered this granddaughter of his so much. Since Marceline's parents died and became orphaned at 6, Grandpa Roland took care of her, treating her not only as a granddaughter but as his own daughter.
Just one request from her, the old man would move mountains just to fulfill her request. Same thing for Marceline, one word from her grandpa and she would not defy him.
