You can either do the quest called "Unfriendly Competition" when you get to the part when you see Agarmir and his friend attack you cause you caught them in the act of getting "Illegal items".

Argamir's friend had the full set of Deadric armor except without the helmet and the shield and he carries a sword.

The other option is to create a killing frenzy or rage spell and make sure it is at least high enough to get them to fight each other or you can get umbra to follow you to the Roxy Inn. Or let her kill all of the people that have the glass and deadric armor (and pray that she will not find you, unless you have a really high sneak). That and umbra might kill them all except Malene.

If you are learning how to master heavy armor do not let Pranal die or you cannot learn it.