Upvote:4
Transiting via Hong Kong might be one option, since the airport reopened to transit passengers on June 15, is easily navigable by a Chinese speaker, and is not subject to the same flight restrictions since it's not considered an "international" destination by China. And indeed, doing a quick sanity check on Google Flights, all available flights from London to Beijing in the next few weeks route through Hong Kong!
Note that, as non-residents, they will not be allowed to enter Hong Kong proper and all the usual methods of overland transit (ferry etc) are also suspended, so they will have to book a direct transit via Hong Kong on a single itinerary.
Update: Cathay Pacific, which is effectively the only carrier you could use, states "During this first phase, there will be no transit services to and from destinations in Mainland China." It's unclear how long "this first phase" will last though, so I'd keep an eye on this.