The comments on here advising you to seek clarification via the Coroner are extremely premature to say the least on the basis of the information you have given, i.e that despite Police telling you no criminal investigation, you then go on to say that further information from your sister suggests foul play may well have played a part in your brother's death.
Even when there is what's called a "sudden death", i.e. person dies of old age, and Police attend the scene, it will automatically trigger liaison between them and the Coroner via a person known simply as a Coroner's Officer. Unless a cause of death was ascertained and a certificate issued by the doctor declaring life extinct, a post mortem would then ensue, and should it transpire that foul play was indeed involved in the cause of death, a full blown criminal enquiry and Coroner's inquest would be required.
Therefore, unless you find out before you return home that a death certificate HAS been already issued, you and your family's first port of call ought to be the Police local to where your brother lived, simply because, unless things have changed in recent years, the Coroner's Officer, who should be based at a main Police Station, would be the involved, as would the Police if anything untoward was suspected.