Jason hires Isaiah, too, to check if his wife is cheating on him, which is ironic since he had been cheating on her right before they even got married.Amanda has no idea that her sister is, in fact, her mother.Jason only got married to Adeline for her trust fund, which only unlocked the minute they got married. He has always wanted her best friend, instead.Mallory has always known about Amanda, Adeline’s daughter. Jason didn't just hire Isaiah at random. He knows who Isaiah is. Has always known. He married Adeline, knowing she had a baby, and even kept tabs on Isaiah just to use him later. Isaiah knows about someone tracking him, but does not stop it. He is curious to know what Jason wants and how Jason knows him. This gets revealed in the plot. When Adeline hires Isaiah, Jason already knows it. He set her up, just waiting for her to fall so he can leave the marriage with the rest of her trust fund, since in the will of her father, it is stated that the only way she forfeits her fund in marriage is if she is unfaithful to her husband. Jason intends to use her feelings against her.Grace forged some papers when Amanda was born, so legally, on paper, Amanda belongs to Jason. This is part of her plans to ensure nothing goes out of place, because she is laundering money through Jason’s company, using Adeline’s trust fund as the cover. She is the one who pushed for Adeline to marry Jason after courting him for a while.