I hope Savanah's baby is Harry's. That is much better storytelling since the woman who has problems getting pregnant does so from a one-night stand, particularly with mixed races, has been done to death. She has a much more interesting predicament over when and whether to tell Harry the truth if she knows the baby is his.
There needs to be something in Karen's history that spikes her attraction to Sam. I can't see a woman as lovely, intelligent, and educated being even remotely attracted to this boy. The father, yes; the boy, no way. Case study, yes; lover, no.