Just as in real life: make friends, get them assigned to you as part of the job, hire them yourself, or, if you’re feeling lucky, blackmail or intimidate them into helping you (and probably backstabbing you or deserting at the very first opportunity).
Social Skills are NOT “mind control”. If they want an enemy to actually obey them, they need to convince them really, really good or threaten them into submission (see above, deserting or backstabbing inclusive).
You can try using Persuade or Command to make a deal with some former enemies. It depends on how strong their dislike for you is. If they were hired help, simply offering them a better deal, more Gold, etc. might do the trick - which would be a Society test. If they are religious fanatics, death cultists, etc. any attempt of swaying their mind might be futile. It depends.
An allied NPC could be anything from a Minion (animal or human), a Toughened up to a Nemesis type NPC.
Usually, the more competent, the more self-willed those NPCs will act.
That means, you can try to make a suggestion on how to act to an allied Nemesis NPC, but the NPC will have own motivations and goals that have higher priority, so they might only consider your suggestion, but do something else entirely, while still being your ally.
This is - as always for NPCs - the GM’s call.
If you have, for example, hired two men-at-arms to accompany your PC through a bad part of Shadizar, they might simply use their Assist action and give your PC’s actions additional successes. Or, if you hired them and paid them well enough, they might take independent actions. That means, they act on their own turn in the initiative and roll their own die (Minions) or dice (Toughened and Nemesis).
In practical terms, when nothing speaks against it, I let the players make the rolls for allied NPCs. They do that for their riding animals, their animal companions and for - mostly Minion NPCs - hired help with little risk and clear objectives.
If the NPCs have their own agenda, I will make the decision about their actions and make their rolls, though they are still allied NPCs.
Allied NPCs are not “puppets” of the PCs who hired or convinced them into joining their cause.
So I tend to play them as any other character.
If the players try to use allied NPCs as “cannon fodder”, send them into traps, etc. they will revolt, they have a sense of self-preservation, and they will stop being allies quite soon (deserting or backstabbing while deserting).