Can I see the red leaves if I went to Xiangshan on 17-18 Nov in Beijing?

Yes, but it may be a little late to view the best view of the red leaves at that time. As per my experience, you's better go there before Nov. 10.

There is around 2 miles between the two universities, so you can take a taxi to reach. Or walk from the Peking University to Yiheyuan Road East Exit to take bus no. 594, 331 oe 508 and get off at Lanqiying. Then you can walk to the Tsinghua in a few minutes.