"Shadow Robotnik." Gerald called him "my son" in Shadow 2005, doncha y'know.
Shadow frostily calling Eggman by his first name. Eggman sarcastically using the phrase "my dear uncle Shadow." Shadow makes a point of acting avuncular towards i.e. Sage and Omega, but not Ivo himself. Someone comments in Eggman's presence how weird it is that his uncle is a hedgehog who is also the Ultimate Life Form and he's just "shut up. shhhhhut up. shut the heck your mouth." Someone in GUN makes a similar comment in Shadow's presence and he's like "I don't seem to recall that the military from which GUN descended gave Father the opportunity to ask for your damn opinion." There's a recurring bit where Eggman and Shadow's dynamic gets framed as "a youth (Ivo) rebelling against an older family member (Shadow)" even though Shadow is both subjectively and physically the younger of the two. (Possibly also chronologically, too -- I interpret the "everyone always talked about Maria like she was special" audio-log from Frontiers as Maria's family grieving for her after her death and Ivo being old enough to remember it happening.)
At the end of Cannon's Core in SA2, Amy says her speech, Shadow gets the flashback to what Maria really said instead of Gerald's brainwashing, and then he turns to Amy and says "Eggman really is Dr. Gerald's grandson, isn't he?" (like, he'd spent the whole game under the assumption that Eggman was just lying to try to get access to him or whatever) and she's like "Uh. Yes? I think so" and then he just immediately goes over to face the Biolizard.
There is just so much untapped potential for Robotnik Family Drama.