I might be wrong but I think this issue has come up before . Mouse over events inside widget blueprints affect the whole widget. So basically if you’re mouse goes anywhere inside the widget it will call the mouse over effect . Hopefully this will be addressed and changed by epic.
I think the solution people have been using is to create a border around you’re button set it’s alpha transparency to 0 then it will be invisible. This way you can have mouse over events for each border for each button .