Final answer:
Without specifying which Philip is in question, the relationship between Conrad of Montferrat and Philip cannot be determined from the information provided.
Step-by-step explanation:
The question regards the familial relationship between Conrad of Montferrat and Philip. To provide an accurate and detailed response, we would need specific information regarding which Philip is referenced here, as there were several historical figures with this name. However, with the information provided, we cannot confirm any direct relation between Conrad of Montferrat and Napoleon's brother putting Joseph Bonaparte on the throne of Spain, which is the context given. Therefore, we cannot answer which of the options (brother-in-law, cousin, son-in-law, or nephew) accurately describes their relationship without additional context.