This answer is going to be subjective, depending most heavily on tomes. Gear and guild level also matter a little, but those can be worked around. Racial Past Lives can also help a little
You're correct that all caster classes require 10+(spell level) in that main casting stat. Lesser Death Aura is a second level spell and Death Aura is fourth, so you need 12 int by level 3 and 14 by level 7.
Guild buffs grant a stacking +2 to all stats, so even if you dump Int you'll have at least 10. Tomes grant a +2 bonus at level 1, +3 by level 3 and +4 by level 7, so if you have a +4 tome you don't need to worry about gear or Racial PLs.
If you don't have any tomes or RPLs, you can still easily cover these bases with gear. +2 ability gear is easily obtainable at level 3 from the auction house or quest drops, and the same is true of +4 gear at level 7. In the short term, you can chug Potions of Fox's Cunning or use a wand - these have 5 min durations so they'll be kind of a pain, but it's yet another option