In regards to selling bikes in Vlad, I'm guessing that the odds are not that great to sell a bike and less to get a fair price for it.
As you may know, Vladivostok is the main importation port into Russia for most vehicles from Asia. There are thousands of second hand vehicles brought in from Japan etc. and driven across to western Russia to be sold. Bikes are also imported, although in much smaller quantities.
The number of bike buyers is fairly small and they already have their own Japanese bike that they have imported or bought off an importer. Most buyers that you would come across would offer you a wholesale price as they would likely be wholesalers themselves. So if you want to simply get rid of your bike instead of riding or shipping it back, prepared to take a beating on the price. The only caveat to this might be the fact that your bikes are BMWs and you might, just might find someone willing to pay the high price for a bike that they can't easily get that far east.
Something to consider is to post here and hopefully hook up with someone who also wants to do the ride one way and have them ride it back or vis versa.