You will never need to implement SizeChangedFcn to all your components.
Put your ui elements inside the containers which are created by uix or uiextrax class as children.
figHandle = figure;
ButtonBox = uix.HButtonBox('Parent',figHandle,'ButtonSize',[100 50]);
buttonHandle1 = uicontrol('Parent',ButtonBox,'Style','pushbutton','String','OK');
buttonHandle2 = uicontrol('Parent',ButtonBox,'Style','pushbutton','String','Cancel');
There are other options for both vertical and horizontally as boxes, panels, etc..
You can read the documentation.