"Which caster heroes have you unlocked?"
Vekk, Gwen, Xandra, Olias, and 3 monks. Could probably get Master of Whispers pretty quickly.
I'm a necro.
Long post, but should work as a guideline for anyone working on their HoM but doesn't feel like unlocking every skill in the game. Basically, always bring the first 4 heroes.
The core of most of the hero team builds is the SoS Rit, Resto Necro, Minion Bomber and Domination Mesmer. If you rule out all of the things heroes are bad at (which is an awful lot) then you'll be left with the 3 Ele heroes. If you can unlock Masters of Whispers then you'll get Sousuke and Zhed in the process so the last 3 slots can be Zhed, Sousuke and Vekk.
Olias:
Death Magic - 12 + 1 + 3
Soul Reaping - 8 + 1
Protection Prayers - 10
Aura of the Lich (Hell's Precipice)
Animate Bone Minions (Kamadan)
Death Nova (Kamadan)
Masochism (EotN)
Putrid Bile (EotN)
Shield of Absorption (Yohlon Haven)
Protective Spirit (Kamadan)
Aegis (Kaineng)
Master of Whispers:
Restoration - 12
Soul Reaping - 9
Whatever - 9
I usually use Icy Veins, Enfeebling Blood and Weaken Armor but since you're a Necro you might be bringing curses already. Smite Hex and Smite Condition? The elite doesn't really matter.
Signet of Lost Souls (Kamadan)
Mend Body and Soul (Kaineng)
Spirit Light (Kaineng)
Protective Was Kaolai (Kaineng)
Rejuvenation (EotN)
Xandra:
Channeling - 12 + 1 + 1
Restoration - 12 + 1
Spawning Power - 3 + 1
Signet of Spirits (Ferndale)
Bloodsong (Kaineng)
Spirit Siphon (Kaineng)
Ancestors' Rage (Kaineng)
Mend Body and Soul (Kaineng)
Spirit Light (Kaineng)
Protective Was Kaolai (Kaineng)
Life (Kaineng)
Gwen:
Domination - 12 + 1 + 1
Insipration - 8 + 1
Fast Casting - 8 + 1
Restoration - 3
Panic (Hell's Precipice) - Use Energy Surge if the mobs aren't big. Psychic Instability is also really good.
Mistrust (Kamadan)
Unnatural Signet (Kaineng)
Cry of Frustration (Kaineng)
Shatter Hex (EotN)
Power Drain (Kaineng)
Waste Not, Want Not (EotN)
Flesh of my Flesh (Kaineng)
Vekk, Sousuke, Zhed:
Air - 12 + 1 + 1
Energy Storage - 9 + 1
Whatever - 9
Thunderclap (most Prophecies missions after Iron Mines)
Air Attunement (Kaineng)
Aura of Restoration (Kamadan)
Shock Arrow (Kaineng)
Lightning Orb (Kamadan)
Chain Lightning (Ember Light Camp)
Prots / Smiting / Command Shouts / Curses / Res
That should roll through most of the content, although having Norgu and Razah would make a huge difference for the more difficult stuff. If anything seems too difficult - and Guild Wars is sure as hell full of bullshit missions - change Xandra's build to:
Communing - 12 + 1 + 1
Spawning Power - 12 + 1
Soul Twisting (Raisu Palace)
Shelter (Kaineng)
Displacement (Kaineng)
Boon of Creation (Kaineng)
Anything