Different phones have different user interfaces, so knowing what phone this is might help. For example, I assume that he's altering airplane mode and DND via "quick settings" buttons or tiles in the notification slide; every phone I've owned has let me choose which settings appear there, so I'd deal with that by customising those buttons so that the settings that are there are not important (so it doesn't matter if they get toggled accidentally). But I can't guarantee that an unknown phone would let me do that.
Volume keys are different. Maybe if you can find a case that makes it hard to press those keys (the opposite of what most want)? In Android 9 the default for the volume key is media volume, which might be better since you won't accidentally turn the ringer volume down, but a phone that's still on 7 isn't likely to get 9 now.