UMG Widget dynamically resize interface elements based on the Screen Resolution to avoid having to code such a behavior by ourselves. It’s good but sometimes it’s hard to wrap our head around it. Hopefully, Unreal provides tons of useful levers to control this behavior.
Your case is an easy one: you want to make proper use of “Anchors” and “Sizebox” or simply the “Size” of your interface elements.
Anchors determine where is the object’s pivot point on the interface so that Unreal can resize him and move him on the screen relatively to his pivot. In your case, I’d say your two bars should be anchored in the middle/bottom of your screen and given an alignment to move them up (alignment is basically an offset based on the size of the item you’re offsetting).
I would also move each bar inside a widget element called “Size Box” and give the Size Box the fixed size I want (one Sizebox per bar).