Q:

How is it Alice's clones can be killed without head trauma, and why don't they reanimate into zombies?

It was made clear in the first film that the T-virus infected dead needed to to be put down by head/brain trauma. I'm unclear on at least two things. First, how is it that Alice's T-virus mutated clones can be dispatched any number of ways, some of which do not include damage to their brains? Second, why aren't the dead Alice clones reanimating into zombies soon after they are killed?

A:

The whole reason that Alice is so critical to Umbrella in the first place, and why she is a central part of storyline, is that the T-Virus does not affect her the same as anyone else. For starters, though she's infected with the virus, she's also alive, without any need for regular doses of the antidote (unlike the girl from the second movie).
Somehow, her body is able to adapt to the infection and prevent it from turning her into a zombie. Instead, the virus binds to her cells in a different way that gives her the above-average strength and senses that she has, as well as her temporary psychokinetic powers (until they are taken from her). The downside is that she doesn't get the same "benefits" as a zombie, e.g. because she's still living, any fatal wound will kill her and the T-Virus won't be able to keep her going, nor reanimate her after death.
Since this is an anomaly related to her physiological makeup, it would also be present in any genetic clones of her. They all keep their resistance/control over the T-Virus. And because they don't reanimate, we can only assume that this resistance is a permanent part of her cellular structure, so it continues even after death.

