So I know Martin Sheen has made several cameo appearances on shows that Charlie Sheen has been the star, Spin City and Anger Management, as Charlie's father. My question has his real life brother Emilio Estevez ever done the same thing?
Question is slightly unclear as to what's being asked, but I've provided several answers below to cover all bases;
If your question is 'have they ever played brothers on film'; then yes. Rated X is one example, wherein the two real life brothers play two porn baron brothers from the 1960s.
If the question is 'have they ever showed up in a cameo role in each others films'; again, yes, more so than the previous. It almost seemed like a game to show up in each others films in the 1980's; Young Guns, Loaded Weapon, Wisdom, Never on Tuesday, Men at Work... the list goes on.
If your question is 'has Emilio Estevez ever made a cameo as Emilio Estevez in a Charlie Sheen text where Charlie Sheen is playing himself (or version thereof) and they make reference to being brothers? I can only say this with 99% certainty, but no. Looking at a list of both their work, there are no films/tv that are metatextual enough for this to plausibly occur.