I'd go economy. $2300 more to travel WT+ or Premium Economy is not worth it as I see it. I think having kids and paying for 4x is the deal breaker. If it was one or two then looking at nicer classes is a consideration, but with kids it's money wasted as I see it. As CSW mentioned the A380 on BA is much nicer in all classes, so if Vancouver is an option that might be the way to go. Good Luck.
PS. As you may have discovered your posts are limited in the initial period after you've joined, so you may not be able to post further for 24 hours.