Answering the questions.

After conversing with Zheng Liang and Yang Ning about Zheng Xiang's return to the palace, the following day, His Majesty announced to everyone in the royal court. He declared that Prince Zheng Xiang would return to the palace after a week and would reside there from now on. While the pretense was that it was time for him to marry and Yang Ning would take the lead in selecting a suitable bride for him, everyone discerned that Prince Zheng Xiang would continue to stay at the palace even after his marriage. 

Though His Majesty didn't explicitly state that Zheng Xiang would stay at the palace permanently after the marriage, everyone understood the underlying implication of his announcement. After all, while Zheng Xiang may be Yang Lingxin's son, he is ultimately the blood of His Majesty and belongs to the royal palace as well.