The four layers are for cycle/velocity/random layering, within each keygroup, I don't think that is what you want at this stage.
You possibly only want a single layer, LAYER 1, for each keygroup within your Keygroup Program.
You first need to set the number of keygroups (up to 128) that you want to use within a Keygroup program, with the NO. KG setting to the right of the virtual keyboard/note range display.
If, for example, you have 3 different samples to spread across the keyboard, you might set the NO. KG to 3.
Then set the SAMPLE(s), ROOT NOTE(s), NOTE RANGE, and other settings, for each keygroup, by selecting and editing each different keygroup in turn with the KG SELECT dropdown list, in the KEY GROUP section to the left of the window.