Tracing RAF Relative
If you believe / know your brother in law is still alive and you / wife have just lost contact, you could write to them via the Disclosures Office at RAF Cranwell in Lincolnshire. Cranwell will not disclose their last known address to you but will forward a letter to this address if you ask them to (Youur brother in law if still present at the address can then contact you if they wish)
If your brother in law is no longer alive, your wife if his NOK can request a copy of his service record from the same office. If your wife is not the NOK (if brother married or parents still alive) Cranwell will only release service record to you with NOK consent.