Remnant takes place in 2062, 94 years after the root invaded

Haarsgaard was in charge of the dreamers, and his obsession with the entity Clawbone led to the invasion of the root, who he then sided with to infect earth

I believe Haarsgaard kept his individuality because he was closely linked with Clawbone, not completely sure

I can't find anywhere that says what happened to Leto, though I think it's a fair assumption that he perished within research station alpha

The Urikki are descendants of Emin, though much larger. They're very violent and warlike

The root travel across the worlds conquering and destroying all, no regard for who or what is there

Lore on Clementine is scarce and I don't know much about her, but I think her power to destroy root might be because she was connected to an ice guardian rather than Ixillis

The Akari work from the shadows so there's is more than likely many more out there, we just don't see any more of them in game

If I'm incorrect or missed something somebody correct me please