Your specs are evolving, or becoming more clear, as the discussion continues. Many of the HI model khukuris of any reasonable length will do what you want. However:
I agree with those who have said that length is not the main factor, that 18" or more is sufficient if other conditions are met. When you speak of "a cleaver with some reach" and "the impact of a crowbar like object, while also being able to stab and slash," what comes to mind is my 18" 37 oz ASTK knife, the older style with the enormously thick chiruwa-type full tang. For a review and excellent photos, try this URL:
http://www.bladeforums.com/forums/showthread.php/742330-My-New-18-quot-ASTK-V
On the question of length, here's a little calculation:
Remember, we're talking about home defense, not dueling against a skilled swordsman.
Suppose your arm is about 24" long, like mine. Add 18" for a khukuri, and subtract about 4" of overlap for your grip. That gives you an effective reach of 38" with arm extended. If your khukuri is 24", the same calculation gives you a reach of 44". The difference between 38" reach and 44" reach is much less important than your skill level and ability to move quickly. And that applies whether you are dealing with one intruder, or two, or a whole trainload of bandits as in last year's story out of India where a retired ghurka soldier drove off a gang of robbers with his khukuri.
Anyway, take a look at the abovementioned photos and ask yourself how much more khukuri help a person would really need -- especially with one in each hand.
-- Dave