Ops, I'm a bit late with this reply.

In any case, the problem resides in the fact that, without mods (or even complete client overhauls like spigot), there is very little difference between an NPC and an actual player. The server will send a "spawn player packet" to the client, which in 1.8+ only contains UUID and server related information; nothing regarding an actual "name" is sent. In addition, without a mod like More Player Models or so, there is no way to alter the behavior of the client getting every skin from the Mojang skin server.

This may be possible with 1.7.10, but even then I wouldn't get your hopes up. Realistically, the best way to go about this is looking for mods (forge or otherwise), and just set up a modded server; without, you'll have to rely on other player's skins.

For reference, the current 1.8.4 "Spawn Player" packet.

bump

Thanks for your help, but I'm thinking custom skins that I made myself to add onto npcs. c:

I think citizens has the options to reskin the npcs spawned so they can wear different skins pertaining to their name.

/npc skin name <- to change the skin

You can also try getting a citizen to wear a head of another player if u want as well.
/npc equip

Sadly, the best that can be done is use an NPC plugin, and change the name to a player with the skin you want. If nothing else, there are many directories with player skins that almost always never change, so those can be a good resource.

Anyways, Citizens is my favorite plugin for this type of thing. Can be a resource hog though, but it has the most powerful scripting out of all options.