1. Why does Ray hate Wendy?
Because he thinks Wendy doesn't belong in Neverland, and should take herself off back to England (I realize she actually does in the books, but I'm going to ignore that little detail. Come up with an explanation of how she got back if you'd like. I don't think it makes much difference, personally)
2. Why does Eric hate Wendy?
She doesn't. I think 'apathy' is a better summary of her feelings towards Wendy.
3. What was with Ray and the mermaids?
To answer that, I'm going to need to write a sequel... it's not easily answered. So...
Epilogue (Or perhaps the Prologue)
Ray stuck out his hand, and Peter shook it. The two boys looked each
other in the eyes, and Wendy could have sworn they communicated far more
than they said. "Some day," Ray said.
"I look foreword to it," was all Peter replied. Then Ray leapt from
the deck, following Eric's course over the island.
"It is time," Roberts said thoughtfully, "for me to return to my retirement."
He lowered himself over the edge of the ship with surprising grace for
a man of his years, into a little boat that had waited, unnoticed, in the
wake of the ship.
Wendy turned to find Peter looking at her, his gaze as intense as Eric's
had been. She threw her arms around him. "How… how did you survive?" she
asked, fighting back the tears that were threatening to flow again.
Peter pushed her away very gently. "My sister. And my best friend."
He turned away from her, looking down at the Lost Boys. "Let's go home,
boys."