Blind diver should have THREE buddies!
....Depends on other conditions or if buddies has Solo diving abilities, Blind diver can have two buddies. Solo-buddy could solve his own problems, and another buddy will stay with blind....
The statement about the Solo-buddy being able to solve own problem is a major fallacy of the solo diving concept. Under most circumstances, a qualified solo diver should be able to sort out issues in the water. However, in the event of a major issue or incapacitating medical problem, a solo diver may not be able to self-assist, and could likely become another statistic. We all like to think we are bulletproof, and even when we take every precaution, circumstances are not always in our favor. Of course having a buddy does not guarantee success or survival, but having a good one will likely increase the probability of a positive outcome.
In this case, though, the Solo-buddy is no worse-off than if diving solo, anyway. (Leaving aside the possibility of becoming involved in a situation, by acting as a buddy in the first place.)
The biggest issue that I see in the whole scenario is that unless the team is using comms, the blind diver is to a large extent a "deaf" diver too. What I mean by this is that communication to the deaf-diver underwater must be through touch signal or a bone-conduction channel. Both are difficult to accomplish rapidly, with complexity, and without immediate proximity. So if one support-diver has to assist the second support-diver in a triad team, the blind-diver is likely to be left almost instantly and at least temporarily un-supported (maybe not a huge issue if conditions are otherwise benign) and importantly, largely ignorant as to what may be going on with the support team. (Going down that road far-enough in severity of the issue {serious medical issue, O2 tox, etc.}, it would be a very complex task for one support diver to perform a full-blown rescue of the other support-diver, while also managing the ascent of any diver under their support. But arguably a very-low-probability event.) Big question - can the blind diver operate without assistance or guidance for a long enough period of time, on their own, without direct support, while maintaining position (well-enough) and without panicking, for the support team to sort things out and get the blind diver back under supervision and communication.
I would think that the 2-support divers should both be fully solo/self-reliant trained/equipped so that almost any issue can be dealt with individually without removing support of the assisted diver. Comms would at also allow the blind-diver to receive guidance and status updates to better allow them to operate, with confidence, semi-autonomously.
If only one support diver was being utilized, that diver should not only be fully self-reliant, but trained to the standard of DM/Instructor in being able to self rescue while simultaneously managing a diver requiring immediate supervision.
Part of it comes down to how good/experienced/self-reliant is the blind diver. Analogy: there is likely to be a big difference between the newly certified OW diver and the 1000+ dive blackwater-experienced wreck diver when SHTF. Maybe a staged certification that allows less supervision as the blind diver progresses ...