@Jag Sofia isn't with Alastair. She's with Jack and Sarah.
Alastair cant do anything otherwise he'll be banished and Sofia will be executed- That makes no sense. If the king was that bad, who would enforce the punishment, yet heel-face turn when Alastair ACTUALLY kills the king? Not to mention Alastair would be a crown prince, so the guards would probably have to follow his commands.
His brother would steal Sofia and hit her- So while I thought Alastair was just giving his brother the benefit of the doubt, he was actually leaving his daughter unprotected. 17 times.
He killed his brother when he learnt that he took down the towns defences- So he commits B&E, and kidnapping, repeatedly: his guards are still loyal. He lowers town defences, which he has every right to do, they somehow decide to side with Alastair?
He hunted Joel down for the next 14 years and he travled to Japan- in which time Joel would wipe Sofia's memories and corrupt her to be totally loyal to him. It's how he operates.
He rescued Sofia and she recognized him when he showed the picture of him and her together- See above.
Sofia willingly killed her mother- she was four. Four year olds don't have the cognitive ability to do that. Plus, Alastair still made her fight.