Well i had bad experiences with umg and touch input.
in umg when you pressed button and then slide touch outside its area button keept shooting and there was no way to fix it. Yes it was 4.20 or so.
To solve whole thing i just detected touch then defined areas (some geometry and math) where buttons and joysticks are.
Now i would just draw texture put it in material, then check if it matches where buttons and joysticks are, then read correct pixels out of if to determine what player is touching.
UMG is bad for arcade games input.