Technically speaking, Ignis, Gladio and Prompto's gameplay don't differ too much from Noctis (outside of his warping) since he can use all their weapons.
So, while I don't expect the actual control of the characters being different (especially in regards to Gladio and Ignis), I expect some differences in how they animate, their stats and so, how you have to approach the combat system. Whether those are going to make the experience significantly different or not, I don't know, but Gladio was said to be more action-oriented, Ignis more tactical and Prompto's DLC inspired by third-person shooters. I wouldn't be surprised if we could attack in a different way than just auto-aim.
So, for example, I don't expect Gladio to be as agile and aerial as Noct (I might be talking out of my ass, but I recall that the journalists that saw a preliminar look of his DLC likened it to Dark Souls -I'm guessing in terms of combat rhythm, as he's a heavier character with only heavy weapons and shields-), or Ignis and Prompto having the same amount of resources he has. They're most likely going to shake the gameplay up a little bit to make up for the losses of warp strikes and weapon variety.
Of course, the "action-oriented", "tactical" and "third person-shooter" terms are most likely more about their respective DLCs' approaches, and not so much about their playstyle, which, at the end of the day, is going to be pretty much on par with Noctis'. I mean, they have to work and complement each other for the online DLC.