It is quite hard to effectively multibox in a bg. Moving around in sync is nearly impossible since Blizz blocked following in BGs, so unless you are talking about someone camping WSG flag room, just avoid the area they are set up.
If they are camping the gy, go to the other side of the spawn. If they are camping the flag room… that’s going to be hard to crack. From my experience as the multiboxing arcane mages in WSG, the only way to get by them is to have three or more people going for the flag at the same time, and all with sprint. Send in the beefiest players you can first, then the druid / flag runner. By the time the mages have taken down the first two, or targeted the actual runner, you are out of los and are home free. Moving all of them is nearly impossible, so don’t expect them to chase you down with any more than 1 of their characters.
Now… if you are facing 3 coordinated players controlling individual arcane mages… There is no hope.