When Keith and Joey were returned to her care, Miranda was ecstatic. Colin was enraged, but then realised he could use them.
All he had to do was pretend to love them and become a kind of psuedo-dad. Then they would do anything to please him.
Colin was correct. By treating them as if he loved them they would believe anything he told them and do what he wanted.
He spoke hard against their parents. He didn’t have much work to turn them against their father, a bit more effort against their mother.
It didn’t take long to plant the seeds of ‘neglect’ ‘abandonment’ and make them believe their parents were the worst in the world, and Miranda was a Great Mother.
Colin kept the propaganda flowing, so they would believe only Miranda and Colin loved them.