Regarding negative traits for elves
I do understand exactly what you are talking about about.
In my current campaign (Sindar Elves) , Thrandul has 2 sons and 1 son-in-law.
While he is Thrandul the Watcher (not a great name, but .. ok) his offspring are .. Nestarion the Mean, Erynion the Mad and ... Legolas the Cruel !?!
What a fine family

I am seriously thinking about giving the position of faction heir to one his many grandsons, whoever turns out to be .. normal.
And I swear that I never slaughtered any prisoners or even sacked a settlement (except 1-2 in the Misty Mountains and in Isengard and this was not even under the command of any of these)
Nestarion and Erynion were actually always governors (Thranduils Halls and Ost-in-Edil) and have never seen battle except once when Nestarion defended with 1000 elves against 4000 Orcs ...
But still it is fine to have negative traits for them as it adds to the flavour. I mean we are all just huma.. ehh elves and as I said hopefully Thranduil will stay alive long enough to see one of his grandsons to be emerging as a new worthy successor. I do have some hope in one the sons of legolas who just successfully liberated Fangorn and Isengard from the evil powers.