They can’t sue him civilly if he’s not convicted.
I'm sorry? How does that work? For instance, OJ was acquitted in his criminal trial but indicted in his civil trial. There's no jeopardy attachment on an acquittal. Civil and criminal are different courts.
They can sue him. A couple of points. The immunity law provides that if a person with immunity is sued, then the plaintiff has to pay the (civil) defendant's costs and damages flowing from defending himself in civil court.
The other point is found by answering "when does immunity attach?" It is supposed to attach at the outset, and preclude arrest, incarceration and criminal trial. None of those immunities ended up being worth spit, because Corey and her minions flouted the immunity law. Does immunity attach as a result of acquittal in a criminal trial? No, it does not. This is a little harder to explain, but I'll try.
Acquittal means that the state did not disprove self defense. Disproof of self defense for acquittal is a low hurdle. If the defendant produces reasonable doubt, then he is acquitted. If there is any theory of self defense that is not proved impossible by the evidence, then the jury must acquit.
But, for immunity purposes, the standard of proof is higher. The defendant has to prove it is more likely than not that her use of deadly force was justified. That finding can only come from a judge, or, from a civil jury. If by civil jury, "immunity from trial" is moot, but the plaintiff is on the hook for the costs and damages incurred by the plaintiff. If by a judge, and this is usually argued to a criminal trial judge in a motion for immunity, the civil trial is likely never brought.