2, maybe 3. Most of Law's abilities can work on anyone, it depends on how sharp and aware Akainu is, something we can't gauge too well from what we've seen but he's been in the Marines for a while now. Meaning he's probably got a decent amount of experience and has probably taken on multiple enemies before. Then again, Law only needs one opening to weaken Akainu. Either chopping him in half or taking his heart and he gets the advantage. With two Laws, I think Akainu would have his hands filled, watching two people who can manipulate space as well.