Again, Ellie is the daughter of the MC, Lucas and Olivia were never together, they were never married and he never laid a hand on her! Just because the model of Ellie looks younger doesn't mean she is automatically the daughter of Lucas. Because the age of Mia and Ellie gets defined by the time the MC was away. If he was 20y away in your version, then Ellie is 19y old. And Mia is DEFINITLY the daughter of the MC, because her mother is Lily, who only was with the MC. Mia is also shown in the prologue. You need proof that Olivia was never with someone else? (SPOILER AHEAD!) Here:
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Even the last scene with Apple and Lucas shows he gave up on Olivia and found a substitute for her (Apple). Only Mia and MC don't know the truth about Ellie at this point. Yeah, Lucas had a thing for Olivia, but that doesn't automatically mean, that Olivia gave in.
In all honesty stop skipping the text and start READING! Heck, even Ellie knows, that she is MC's daughter. Why would she call him daddy otherwise? Why can't you just accept the facts given to the player?
Read my text above, please.