So I've never been a huge lore guy in games but I've noticed a few of the deeper connections between champions in the game and I'm curious as to the ones I've not discovered yet.

Here are the ones I know so far:

Cass and Katarina are sisters.
Draven and Darius are brothers.
Jayce and Viktor are bitter enemies.
Volibear and Zilean have no respect for each other (Developer joke I know)
Ashe and Sejuani are direct rivals for the title of Queen.
Renekton and Nasus are brothers.
Kennen, Akali and Shen are all from the same clan.

Eager to hear the rest.

Morgana and Kayle are sister that hate eachother.

Isn't Tryndamere married to Ashe?

One I'm extra curious about. If Ashe and Sejuani are the descendents of 2 of the 3 sisters, what if any champion represents the 3rd?

Rumble is in love with Tristana, but he's competing with Teemo, although Teemo has basically been friendzoned.

Graves and Twisted Fate used to be gambling buddies until TF sold Graves out for magical powers
Urgot was revived with Viktor's works (Viktor also created Blitzcrank)
Soraka cursed Warwick, turning him into a werewolf but also making her a unicorn.
Singed's work destroyed Master Yi's Village
So much more.

You forgot (But I know you know (?)) Garen and Lux are brtoher and sister, and, if I'm not confused, Sion Killed Urgot.. if not... please let me know my error.

Also, Pantheon and Leona are friends, or used to be friends I'm not sure.

http://www.youtube.com/watch?v=kWRJcL9IjJQ