making bodyparts instead of whole Persons

I've thought it would be better if instead of making 10 different persons to split the model into parts and then model the parts differently. That way it would be possible to make a ton of different characters from the parts.

What I would like to know is, if the parts would be used for a game, would I need to put them together in an editor/modeling software before I use them or is it possible to put them together through the game engine?

I'm not experienced much in game dev but I suppose you should put them together before you'll import them to game engine.