If you tell Halsin about Oliver, he normally wants to come with you. He talks to Oliver and then things happen, don't want to spoil you too much. I would go back to him, tell him, what you found and then he should go with you or meet you there, I don't remember, if he joined me or got there on his own.
I' ve met Oliver before it was clear, he was Thaniels other half and played hide and seek, fought mother, father and the dog and then it didn't advance. Until I talked to Halsin about it.