Any suggestion on our tour in Shanghai, Guilin, Xian and Beijing?

I have booked our air flights for my wife and myself using my aeroplan points.
We are departing on April 27 to Shanghai and returning May 22 from Beijing.

Here is what we would probably like to do but its certainly open for suggestions:

- 3 in Shanghai
- my son will travel up to Shanghai from Li Xien (Wenzhou region) and meet us
- travel to Guilin area - 3 to 4 days (all 3 of us)
- return to Li Xien for 3 days - my son goes back to work.
- travel to Xian for ~ 3 days
- travel to Bejing and surroundings ~ 4 days.

There are at least 7 extra days still available so we have not decided what we should do. I like the idea of traveling in more depth in an area and not to try to cover too many separate destinations. However we are open to suggestions. Maybe the Yangtze river or maybe an area farther to the west.

Since we are pretty flexible except for the first week when we need to coordinate with my son and his vacation days which are around the national holiday.

We don't mind traveling with a small group if you want to suggest that for some part.

Look forward to your proposal.