So, it sounds like Allies ought to be defined much like Minions, with weapons and Harm points. Because Allies are under the Keeper's control, it's easy to prevent abuse - Allies only trigger Keeper moves when the Keeper feels it's appropriate. If a Hunter orders their Minions into the fray, the Keeper gets to decide if that triggers inflict harm, as established on the Monster, Minions and/or the Allies in return. When a Hunter asks their Allies to do something that they might not want to do - like wrestle a werewolf - it may trigger the manipulate someone move, possible resulting in the Ally refusing, or demanding a concession in return. If a Hunter callously lets their Allies get hurt, it's likely to affect how their surviving Allies will feel about the Hunter - as well as affecting the opinions of onlooking Bystanders and other Hunters. That could easily trigger a Keeper move like take away some of the hunter's stuff, when the surviving Allies tell the Hunter to shove it and walk off the job (or become embittered Minions of the Big Bad).
In a fight, if the Allies fight alongside the Hunter, it's appropriate to add their weapon damage to the Hunter's damage (maybe +1 per extra Ally?) during kick some ass - but it puts the Allies in the line of fire of any Harm coming back in return. (As described above, a Hunter that treats their Allies like a disposable hit point buffer isn't likely to have Allies for very long. And dead Allies definitely don't get automatically replaced.)
If an Ally is fighting separately (or doing any other task without acting alongside the Hunter) then the outcome is pretty much a Keeper call. If the Hunter stations an Ally to guard the back door, and the werewolf flees through that door, then it's the Keepers call if the Ally inflicts harm on the werewolf, the werewolf inflicts harm on the Ally, or both, or some other combination of Keeper moves. If an Hunter sends an Ally to ask around for rumours in the bars, it might result in the Keeper revealing future badness, revealing offscreen badness, or using a threat move to capture or hurt the Ally. Because the results of an Ally's actions are in the Keeper's hands, without the buffer of the Hunter's moves, it ought to tend to discourage Hunters from trying to 'outsource' their challenges to their Allies. Allies are certainly useful, but they are much less reliable than doing the job yourself. Because of these limitations, I don't think an Ally's stats or weapons are especially critical to game balance.