Good news. Either 33-296-195
(LX Triple Stand) or 33-323-200
(DS100 Triple) will work for your monitors. To be clear, the 20" monitors can only be in portrait, which is your plan, but you won't be able to switch them to landscape. Personally I'd go with the 33-296-195--you'll have nice adjustment options with in-tandem screen tilt and height adjustment. It makes a real difference.
Regarding the LX Arm configuration I suggested, it turns out this config would be outside the maximum specifications like you suspected--your 30" display weighs 21 lbs, just over the listed capacity of the standard LX, and also the three monitors together weigh 44 lbs total, which again is over the guaranteed maximum for the Dual base. There's a decent chance that it would work BUT it won't be guaranteed under warranty because the weights exceed tested limits.