Solution with keyboard shortcuts is probably not possible (not to my knowledge).
But that's the part where tmux command takes part.
For example in my setup I want to open two side panels along with main pane.
I'm using following with Guake terminal:
// Rename tab to current path
shell.exec(`guake --rename-current-tab=${path} &`);
// Open new horizontal pane
shell.exec('tmux split-window -h');
// Open new vertical pane under pane that was created above
shell.exec('tmux split-window -v');
Here you can find a cheatsheet for tmux commands: https://gist.github.com/MohamedAlaa/2961058