From Harry Potter wiki:
They are probably people that Harry didn't recognize or just didn't know well enough to comment. I'm sure he would have said something if it was any Gryffindor 7th year boy or if it was Lavender or Parvati. It could be one of the unidentified Gryffindor girls, or memebers of other houses that Harry didn't really know. It also didn't say they were human, so it's possible that a house elf or two were killed. Harry didn't know all the order members, so its quite possible it was some of them.It is likely most of them were adults of at least seventeen years old, as Harry Potter did not see anyone he recognised dead, besides those he named. It is likely that half of the fallen would have been fellow students, the rest possibly members of the Order of the Phoenix, staff members, or residents of Hogsmeade. There may well have been even more casualties than just fifty, but the bodies of these may not have been collected at that point, as Colin Creevey's body was discovered out on the school grounds by Oliver Wood and Neville Longbottom and as Hogwarts is such a large place it is unlikely that all bodies were retrieved and brought back to the Hall during that phase of the battle.
It could also be that they are people we know, but JKR didn't mention them simply because it wouldn't have any effect on the audience, as Fred, Lupin, and Tonks, who are pretty well-known and loved characters, or the death of Snape and the Pathos that is generated given his situation, or Colin, which is almost a loss of innocence or the tragic waste of young life, the reason we feel for him is because he "looked so small in death", and we remember the small, loveable, annoying First Year from CoS. Yet any character with a name would have an effect on someone somewhere.
I"m more inclined to think that they were all unnamed characters, simply for that reason. Other students, people from Hogsmeade, Order Members, Proffessors that Harry never had...
I would think that Ernie is a no, because wasn't he with Luna when they produced Patronuses? And for proffessors, maybe Proffessor Vector as we never actually meet that Proffessor.