Nicely done! The concept is cool, the behavior of the siblings is interesting, and the gameplay is very interactive, requiring a bit of planning ahead and escape maneuvers in order to "win" (or at least break even). I like to think that every time you win you're not actually shrinking, but competing with equally massive beings from a further zoomed out perspective.
I really like how the siblings are dynamic and will choose to chase down smaller siblings or run away from bigger ones, but I noticed in the early stages that "dances of death" would regularly happen, where two equally sized siblings will pair up and endlessly circle each other. I had a game where every sibling paired up like that, leaving me free to eat the entire board unopposed. Perhaps a bit of randomness in their behavior would help with that?