The simplified forms of the composite functions are \((f \circ g)(x) = \sqrt{x - 2}\) and \((g \circ f)(x) = \sqrt{x} - 2\), with their domains being \(\left\{2\right\}\) and \(\left\{4\right\}\) respectively. At \(x = 6\), \((f \circ g)(x)\) evaluates to \(2\) and \((g \circ f)(x)\) evaluates to \(0.45\).