PSIII Castle Question

I don't remember, so I'll ask the collective: Are the castles in Lensol, Techna, Divisia, and Mystoke ever shown to be inhabited? I know some of them are empty when you go there, usually to find something or someone.

Three are abandoned...

Lensol was apparently overrun and captured by Siren's army who kept Thea prisoner there.

Techna castle is where Siren's army is entering through so it's also abandoned (yet the town seems to be fine).

Mystoke is festering with monsters, likely to guard Laya's Pendant.

Divisia castle is inhabited - there's a dialog with the king and soldiers who are keeping Alair prisoner.

Another question: At which point in the Ayn timeline is Satera is destroyed?

It's never specified. The only one who even references the fall of Satera at all is Alair, who says, "Yes, we were the ones who destroyed Satera. But we're not behind the recent monster attacks."

Although Nial and Ayn are a couple years apart in age, I think there's enough conjecture to assume that their stories occur roughly in parallel.

Ooh, Alair admitted that the Layans destroyed Satera? Interesting...

Yep, that's part of her standard third generation dialogue. From that, we can tell that Lune's forces made it at least that far into Landen dome. It makes the narration that says Ayn and Sari defended their home without fail a bit strange, though. I'd say losing Satera was a bit of fail, myself...

I assumed Sari already lost Satera during or before Ayn's quest.

Ayn: That's right, we defended Landen Dome without fail! >=D
Sari: Umm, Ayn? Satera got burned to the ground.
Ayn: Well-
Sari: And Azura got blown up...
Ayn: Look, that's-
Sari: And our son... well, look how he turned out, Ayn!
Crys: Heh heh heh heh! Chainsword GOOOOOOOD~! (waves arms around) BZzzzZZzZzzzZZZ!!!
Ayn: Is this really my fault?
Sari: I don't remember using swords.

I can imagine Lune taking advantage of Sari's absence to attack.