Don't know. Not sure it matters, really. In that scenario, they could have the same rank, but one could occupy a senior billet and therefore have supervisory capacity over the other.
You're right, it doesn't matter. I'm just one of those guys who likes to know what rank all the Starfleet officers hold. And unless you say otherwise, I'm going to believe they are both full Admirals.
Several Rear or Vice Admirals (including Pressman, Nechayev and Fujisaki (as Deputy Director) have been mentioned as part of Starfleet Intelligence), the only 4-star admiral seen as part of SI IFAIK was the Udine recreation of ADM Gareth Bullock suggesting that he is SI Director. If so, it's likely that the head of SI for Earth/Sol System is junior to him (The ONI Director is I believe typically a RADM).
In addition to ADM Bullock, I believe Uhura is a four-star admiral in Catalyst of Sorrows. Speaking of Uhura, I was under the impression that she retired in 2360 at the end of the novel, but then in the Vulcan's Soul trilogy, she was seen still on active duty in 2377. Is this simply a case of the Vulcan's Soul wanting to use all TOS characters or just two separate continuities?