If you use TextureRect nodes, TextureButton, or any other Control-based node, you can take advantage of Godot's layout system, which will allow you to have items positioned relative to the screen size. You will also need to make the root node (Titlescreen in the case of the picture) a Control node as well, with a layout set to FullRect, and I would recommend doing this before converting the buttons so the anchors are correct.
You can read more about Godot's UI layout and anchor system here on the documentation.
