Howland arrived at the end of the stairs to check on his sister's condition. He didn't come down because he knew that if he got closer, his resolve would collapse and he would run to hug his sister regardless of who the soul was in the body right now.
Howland didn't want to betray his real sister like that. That was why Howland would keep his distance from Rosie until it was completely clear who the perpetrators were and what they wanted.
A knight opened the carriage door. Then, Rosie, still in her nightgown, got off the carriage and looked at him straight in the eye. Howland looked at his sister carefully, making sure that there were no wounds embedded in his sister's body.
After making sure that his sister's body was fine, Howland then left Duke Coby's courtyard just like that. He walked straight to the meeting room so he could talk to Rosie for a moment.
He waited by the window for Duke Coby to bring Rosie closer to him.