I found this a Youtube Video comment. This is a cool thing to base my idea from.

Ayato=Pride: Because his arrogance
Shuu=Sloth : Because he is lazy
Reiji=Envy : He is envious because his mother preferred his brother Shuu.
Laito=Lust : Anyone know why xD
Subaru=Wrath : Because his outbreaks
Kanato=Greed : Because he is greedy to get noticed.   

So I got an idea. What if they had servamps or Homunculi that matched their sin? This is what I got:

Ayato=Pride: Because his arrogance.

His Servamp:

His Homulculus:

  Shuu=Sloth : Because he is lazy. 

His Servamp:

His Homunculus:

  Reiji=Envy : He is envious because his mother preferred his brother Shuu.   

His Servamp:

His Homunculus:

  Laito=Lust : Anyone know why xD

His Servamp:

His Homunculus:

  Subaru=Wrath : Because his outbreaks   

His Servamp:

(Looks like Cordelia o_o)

His Homunculous:

  Kanato=Greed : Because he is greedy to get noticed.  

His Servamp:

His Homunculus: