I'm sorry to tell you that the messages are gone. I won't be surprised if "new members" create accounts just to tell you that some dodgy utility can recover them for you, but I can't recall any report of success that was clearly independent of the provider of the software they are recommending. So I really don't think there's any hope of recovering those messages.

Did your local "specialist" root in order to recover messages? There's a certain limited sense in that in that it gives better access to the part of the storage where the messages are stored - they would certainly be irrecoverable without. But if they deserve that title at all they'd have known what unlocking the bootloader would do (they probably unlocked in order to root rather than the other way round). Perhaps they hoped they'd be able to run some data recovery afterwards (which, if so, clearly failed), but if that was the case they really should have explained it to your brother first and ensured that all of the current data were backed up first. To do anything less is completely amateurish.

I assume that your brother did not sync his contacts with Google? If he did then he should be able to restore them at least by just logging into his Google account and enabling syncing again.

 

why would they root the device without your consent....this does not make sense to me......seems kind of shady to me,.