I travel frequently between PEK and LHR (and the US) and it still deals me with a bit of a body blow, jetlag-wise for at least one day. I know that the OP wants to maximise the flight as part of a long week-end, but I'm still not sure it's going to be the best use of time away from the kids.

Want to watch movies and have a nice drink: do it in a 5 star hotel closer to home!

I can't recall when the trip is planned, but in the summer, I would think all three cities are pretty unpleasant. Although beijing is less humid, it is still v. hot and humid compared with the UK (up to 40C in a v. unforgiving sun -- and all the tourist areas are outdoors).

Re: Jenbel and flying times -- it's much more than LHR- US east coast, but 8.5-9hrs on average in my experience (but haven't timed it formally).

tb