The animosity was when Billie and SA first got together. Hailey did want her parents back together, and she saw SA as standing in the way. And no, he did not show anger towards her (that I know anything about).
I am sure there were plenty of times that either of this kids were alone with SA.
This is a hard question to answer...all kids at some point or another have some type of issues with their parents/stepparents/parent's GF/BF. No issues out of the ordinary that I ever knew about.
BBM
Difficult, no, impossible for me to believe the maturity of that young man with the way he comes across in various media. Such control he exhibited at home!