1) there are certainly suggestions, both within LoTR and other writings (UT for
example) that Imrahil's line has some sort of Elvish blood mixed in. But
this also represents the often completely sincere tendency of leading families
to claim "fantastic" origins. Julius Caesar for example and his family
claimed descent from Aeneas (of Fall of Troy and all that) and also from the
Goddess Venus i believe.
2) Legolas has never come across as one of the leading "strategists" or leaders
of the war effort. I don't get much sense he's interested in that sort of
thing.
As to the possibility of Civil War, Denethor's er, untimely, demise has
eliminated the immediate possibility. And until the war with Sauron is
complete further dynastic struggles seem rather pointless. Frankly, if
Aragorn succeeds he will be made King by acclamation, and if he loses noone
will be around to really
care.
