Depending on the levels of your characters I think this is an interesting monster. As it is a brute I am going to assume that the PCs will be about level 7 when they face it.
1: Hypnotic Breath.
This is a pretty nasty attack when you consider that the PCs will have 2 of these to deal with, and then another 2 when the creature(s) are bloodied. This is one of those powers that is quite hard to properly judge; attack +11 vs. Will should hit reasonably well, no problems there. Then we have the fail the save vs. Dazed and drop unconscious, I am assuming that other characters can wake someone up with say a DC15 heal check or the like. This power has the potencial of taking half your group out of action for an indeterminate ammount of time, I am not saying its unbalanced, I am just saying you might have to be careful with it or give the PCs a opportunity to discover this information before its too late. This is one of those powers that can go horribly wrong either way, either you don't get anyone and its a waste of time, or you could get everyone and thats your group dead.
2: Devour Soul.
I would probably make this attack target Fortitude instead of AC as that seems more appropriate to me. 10 healing seems a bit low, as it might not get chance to use this power that often (if at all!!) I would change it to either a straight 24 or more likely heal the ammount of damage dealt. Not waking the person up seems a bit harsh, maybe when hit by a Devour Soul attack they can make a save as a reaction, on success they wake up.
3: Morning Star.
This looks fine, personally I would increase the push to 2 squares.
4: Pommel Smash and Shadowy Rebuke.
These seem good, reactions to melee, close and ranged attacks should surprise your PCs.
5: Chained by Fate.
I like this, 4 squares doesn't give them the opportunity to move around much but that works well with the theme of the creature. I think the players should be able to exploit the chained aspect, and if one creature is forced to move more than 4 squares away instead of just nullifying the excess have it knocked prone. This would reward the players for clever use of powers and give them a brief advantage.
As this is a linked creature have you thought of maybe it having an attack that uses both of them at the same time, If the first one delays until the second one would act (for that round only), then they both attack the same target? Might be worth considering, though it might be a bit fiddly to use.
You also said that there would be some minions involved in the encounter, can you give us some details of them and their number?