The best friend had other motivations than psycho-lesbian jealousy - she was trying to avenge her father who'd taken the fall for financial illegal stuff Emily's father had committed (Emily's father being long dead in the story, so that's why she attempts to get Emily condemned instead of directing her vengeance at Emily's father).
A kid who's lost at least two fathers, is used as a chesspiece by a guy motivated by parental loss?
The kid only lost one father, his. His mother's other husbands both died during the honeymoons, and IIRC he's not mentioned as having been as close to them as he was to Dick. As for Dick's behaviour regarding the child, his sympathy toward him and the fact that he genuinely cares for him is shown and told both rather clearly imo; where do you see he tries to manipulate the child?