An ambiguity of separation of cascades from "pure"\;two-photon decay is confirmed with accurate numerical calculations in a gauge-invariant way. A direct evaluation of two-photon decay width of excited states in H-like ions via the imaginary part of two-loop self-energy is presented. We demonstrate that there is a fundamental difference between the level width and the transition probability in the presence of cascades. The two-photon widths are shown to be different from the two-photon decay rates for the transitions including cascades.