Okay first off, your wording on most of the cards is not the way they would be worded on actual cards. Look at real Magic cards and study their wording.
Ambush: Should only be playable during the combat phase; the way it's written it's a Hideous Laughter in red or white. Also makes more sense from a flavor perspective.
Angelic Siren: "Do not untap during their controller's next untap step" is more green or blue. For what she does and her P/T, she also needs to cost 3 or 4 more. Either that or make her ability cost XX. Either way she needs to cost more. And she needs to tap to use her ability.
Arcane Spell Book: Artifacts are ALWAYS colorless. Also, the last two sentences are unnecessary. Make this an enchantment.
Breech: Instants ALWAYS need a color. I'd say make this red. Also how long does this last? Until end of turn?
Dark Assassination: This is more of a white ability. Remove the restriction and it's fine. Why is green in the flashback cost? It doesn't make sense from a flavor perspective.
Dark Sacrifice: This is your best card of the lot. Appropriately costed, and BALANCED.
Defending Honor: Wording is ambiguous. Are you looking for a Coat of Arms effect? It seems that way. Also, this card should cost WW less.
Heavy Gale: Good idea, but white only gets defensive bounce. Make it just green.
Immolation: Did you mean this to be an instant? Because this thing SUCKS as a sorcery. Blaze sucks and it's this same thing except no sacking a land.
