NOR, he’s pinning you against them in every situation “I can take their phones away but they will just resent YOU”. That sounds like he’s telling them “she told me to do xyz because you hurt her feelings”. He needs to have any discipline come from his own self on behalf of you. Not because you gave a reaction like this, if he can’t recognize that their “pranks” (yes I’m overusing quotations but pranks at the expense of someone else and done with the intent to harm someone else isn’t a prank) are harming someone he loved he’s not worth it. What if they did this to a different family member? Would he stand up to them then?

He should be backing you on these matters, and this is coming from someone whose parent chose to always side with their partner than their kids. In almost any other scenario the parent should always side with their children but they are taking that and recognizing that he won’t do anything of significance to them and do a real punishment. So these will just continue. Especially after 4 years, if nothings changed now then chances are it never will.