This is pretty trippy. Strap in.
5 spatial dimensions.
Imagine 1 dimensional creatures. They lives along a line. They move along it left and right: the only two directions possible. From a Flatlander two dimensional perspective outside the line we can see them moving left and right along their line. Flatlanders also move back and forth in their 2 dimensions.
From a three dimensional perspective we can look at the line like a Flatlander. But we have up and down and we can rotate to see all the 1 dimensional creatures in the same space, overlapping. By coming up and looking down onto their line the line becomes a point, and all of the 1 dimensional creatures are in the same dimensional space.
Now the trip. From a 4 dimensional perspective we can see 3 dimensional creatures like ourselves moving around in our 3 dimensions. But from a 5th dimensional (5th spatial dimension) perspective we can see that all 3 dimensional creatures are in the same 4d space - overlapping each other from this perspective, just as the 1d creatures overlap from a 3d perspective.
Your hive mind uses this. They all overlap with each other from a 5th dimensional perspective, and also overlap with everything else in our 3d universe. It is noisy, all crammed in there together with all that there is. But even in a noisy party I can hear you if you come up close and shout into my ear. If you were actually in my head, you would not need to shout. You would think thoughts right into my head and it would be easy to hear. That is how their hive mind works. Their minds are in different 3d spaces but not different 5d spaces.
3 spatial dimensions and 1 temporal dimension... and 1 more dimension.
The prior considered a 5th dimensional perspective in the context of a 4th spatial dimension. But if the 4th dimension is time, then what is the 5th? From that perspective, everything has happened at the same time. If you can communicate from a 5th dimensional perspective all of our discussions have happened at the same time. I hear everything you have said and everything you will say, now, always.
How to use that against them? For all spatial dimensions, the prospect of creating technology to duplicate 5th dimensional awareness is daunting. The prospect of coopting, or tricking, or hypnotizing one of these creatures and using the creature itself as the entry point... somewhat less daunting.
If the 4th dimension is time, the prospect of defeating a creature for which all times are now is even more daunting.
Hopefully Team Earth is any the top of their game...
Dluz glared sullenly at his handful of pretzels before shoving them all in his mouth. Once his hands were free he began to wave them about. "5th dimension? Everything in the same place?" Pretzel fragments sprayed freely. "I feel a seizure coming on just trying to think about it. How can the Hive do it?"
Peg phlegmatically picked pretzel pieces off his arm and set them in a small pile. "They're big," he offered. "Big brain."
Yesno looked over her shoulder, her hair wreathed with smoke from the grandmother board. "It's not how big it is. It's what you do with it." She winked at Peg. "You of all people should know that, Peg."
Peg nodded as he was showered by a laugh of wet pretzel fragments. "Yes. Yes I do."