I'm making a separate post because I have my own suggestion for the defender;

Firstly take a Human Blackguard or Slayer. These are both considered strikers, but have a parent class of a defender. This gives them tough defenses, access to decent (great with the Blackguard) armor, and decent HP.

Being human gives you an At-Will with the Slayer (Which otherwise gets none), or Virtuous Strike with the Blackguard so you have a tough, feat supported MBA.

Next, PMC to Swordmage. This will let you trade an At-Will for one from your second class. Since the Aegis of Assault is built in the form of an At-Will, it's fair game. With the Slayer, you'll have to trade your human At-Will for it.

The mark punishment for the Aegis of Assault lets you make an MBA on any marked target who attacks someone other than you.

With the Blackgaurd, you're going to make yourself run thin on stats, However, you can pretty much go all Int and Dex with the Slayer.