Rhaegar-Night's King Parallels

[Wunjō]

So there are a lot of parallels between Rhaegar Targaryen and the Night’s king:

1.       Stole a queen of ice (Lyanna)

2.       Was put down by a close relative (Robert was Rhaegar’s cousin)

3.       Sacrificed children (Rhaenys and Aegon could have lived)

But what does this mean, also what other parallels mater?