In the first chapter, it was mentioned that the other charred body was identified as beglonging to Randoh. However, that would mean that they thought Randoh was whoever it was that actually died. As this was never mentioned again, we can only assume that the other guy didn't have a family (that cared).
The issue of Rando's voice is never directly addressed, even when Dr. Manabe supposedly transforms him back into his real self.
Why would someone assume that he was female and rebuild his face like that when he was biologically male? Surely they could have used dental records or something to ID people correctly.
Well Manabe's weird to say the least. He admits in the first chapter that he knew Randoh was male, of course, but thought being a girl was more appropriate as he worked to fix Randoh's face. In fact, Randoh even wakes up in chapter 1 just as Manabe was getting ready to give him a sex change procedure.
The alternate ending was to have Randoh's actual family revealed as getting surgery from Manabe and winding up as Kurumi's family, but the creator dropped it for this trope when he released he'd leave too many plot thread hanging ("Rina" being able to deceive her friends, Randoh's parents knowing about Yuna's run away, blah blah blah..