A thought between Toroko and Arthur

Well...

"Like my brother. He killed my brother!" - Toroko

And then..

"Here sleeps the noble Arthur, the true hero to the Mimigas." - Grave

...Could they be a sister and a brother?

Isn't the King's protectiveness for Toroko even more proof of this chance?
And Sue stays at Arthurs place, Toroko is the only friendly person for her?

 

The game explicitly states that Arthur and Toroko were siblings.