Not necessarily Buff Up, as I was thinking it was in addition as well. Mechanically the Paladin (@3rd) gains Bonus Spells and One once/short rest powers from a choice of 2. So we need powers that are either:
1) equivalent 1/short rest powers
2) slightly weaker At-wills
3) Slightly more powerful usable 1/day
So with that said...
This original version you had...
This is already an improved version of the warlock's "Pact of the Blade", getting to summon as a bonus action rather than an action, and dealing necrotic damage vs normal weapon damage, and lastly can be a ranged weapon versus only melee. I'd honestly say that its a good enough At-Will ability as-is to replace Channeling.
As above, I think the Undead Pet is a decent at-will feature trade for Channeling.
This one I'm on the fence with. You've given them an at-will ranged spell attack. Now you are in effect giving them fighter's 7th level War Magic ability at 3rd level to boot. I somehow feel that is too OP to be getting at 3rd level.
Perhaps this:
Fiendish Legacy - At 3rd level, you gain one of the following cantrips as a known spell that is always considered prepared: Acid Splash, Chill Touch, Fire Bolt, Poison Spray, Ray of Frost, Shocking Grasp.
Additionally, you gain resistance to two of the following: cold, fire, lightning, poison.
Fiendish Talent – At 7th level, when you use your action to cast your fiendish legacy cantrip, you can make one melee attack as a bonus action.
