How to create a panelwidget which can change its childrens' alignment by its detial panel?

I’d like to create a panel widget class based on one of Upanel classes(what I choose is UOverlay), and I want to change all its children’s alignment by changing the panel widget’s detail panel without clicking “Play” Button on the editor.
I simulate the effect I want by BP(I can code this by c++, but BP is fast) Here are some pics.!

Sorry, I dont konw why i upload 4 pics but it displays only 2 of them. So i reuplaod them. And look at my BP Code, all panel’s children widget should be as one widget to ajust their alignment. So I use a Horizen box to contain them as one widget.

you want to use the Construction script so that it would update the viewport when you change values while editing