Leslie, thank you for replying. Yes, they do have several trunks, so looks like I am a bit late with a standard shape. But I need to do something – they will soon block the entrance. I will try Cloud pruning – unless you can recommend something else.
If there is a straight trunk among the bunch, you might be able to cut out one trunk per year until you are left with just the one that you prefer. The trick is not to remove more than one third of the plant per year. I would do this major pruning during the late winter/early spring. But I like the cloud pruning idea.