Here are eight possible reasons why your skin isn't showing:
- Your skin has not refreshed yet. (If you're playing Minecraft 1.7 or above)
- You never had a skin prior to the UUID update, which changes the way skins are stored (If you're playing any versions prior to 1.7)
- You're not using a legal version of Minecraft, and therefore - Your skin isn't registered to your account.
- The server you're playing on has
online-mode=false. (Set to offline mode; no authentication)
- You changed your
char.png file within the minecraft.jar and not uploaded it to your minecraft profile.
- You've uploaded it to your http://minecraft.net profile, but it's the WRONG dimensions (bigger than 64x64 pixels)
- You're playing in offline mode.
- None of youse have an internet connection.
- You may have a bad internet connection and thus timed out or received incomplete information.
For #1, you'll just have to wait, and/or restart your game.
For #2, there's nothing you can do.
For #3, buy the game!
For #4, you should consider playing on servers that only allow 'premium'/paid users.
For #5, you should probabally log into http://minecraft.net.
For #6, you'll have to scale it down. Sorry :/ Unless you get the HD skins mod.
For #7, go online!!! (Same goes for your brothers)
For #8, you'll need to be connected to the internet in order to retrieve skins.
For #9, nothing I can say apart from the generic "get better internet" or "clear off your bandwidth by downloading/uploading less (ie. Stop watching YouTube on 4K whilst others are gaming)".
Very likely, based on the information you've stated that your problem is #3.