If a person dies due to failure of his digestive system then he is a shaheed (martyr)
Question

                My question is about the types of martyrs, as one of them is the one who dies of a stomach disease. I have a brother who died two days ago because his heart stopped, as it says on the death certificate, but everything in his body had failed before that, from his kidneys to his liver, and even his digestive system was no longer working. Can he be considered as one of those who died of a stomach disease?.
Praise be to Allah.Al-Bukhaari (2829) and Muslim (1914) narrated from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The martyrs are five: the one who dies of the plague, the one who dies of a stomach disease, the one who drowns, the one who is crushed beneath a falling wall, and the martyr who is killed for the sake of Allaah.”  
Ahmad (23804), Abu Dawood (3111) and al-Nasaa’i (1846) narrated that the Prophet (peace and blessings of Allaah be upon him) said: “Who do you regard as martyrs?” They said: The one who is killed for the sake of Allaah. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Martyrs are seven besides the one who is killed for the sake of Allaah. The one who dies of the plague is a martyr, the one who drowns is a martyr, the one who dies of pleurisy is a martyr, the one who dies of a stomach disease is a martyr, the one who is burned to death is a martyr, the one who dies beneath a falling wall is a martyr, and the woman who dies in pregnancy is a martyr.” This hadeeth was classed as saheeh by al-Albaani in Saheeh Abi Dawood. 
It says in ‘Awn al-Ma’bood Sharh Sunan Abi Dawood: 
The one who dies of pleurisy: this refers to a pustule or pustules that appear in a person’s side, then they open up and the pain lessens, and that is at the time of death. One of its signs is pain beneath the ribs and difficulty in breathing, along with persistent fever and coughing, and it occurs more often in women. This was stated by al-Qaari. 
Stomach diseases refers to diarrhoea, dropsy and pain in the stomach. 
A woman who dies in pregnancy: al-Khattaabi said: This refers to a woman who dies with a child in her womb. End quote. 
Al-Nawawi (may Allaah have mercy on him) said in Sharh Muslim: The one who dies of a stomach disease refers to diarrhoea. And al-Qaadi said: and it was said that it is the one who suffers from dropsy and abdominal swelling. And it was said that it is the one who suffers from a stomach complaint. And it was said that it is the one who dies of stomach disease in general. End quote. 
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked: It says in the hadeeth that the one who dies of a stomach disease is a martyr. What is meant by the one who dies of a stomach disease? Does that include one who dies of cirrhosis of the liver? 
He replied: The scholars said that this refers to anyone who dies of a stomach disease. It seems that it also includes those who die of appendix problems because these are also stomach diseases that can kill. End quote from Fataawa al-Shaykh Ibn ‘Uthaymeen for al-Da’wah magazine. 
Based on that, if your brother died because his liver or digestive system failed, then there is the hope that he attained martyrdom. 
We ask Allaah to forgive him and have mercy on him and raise him in status. 
And Allaah knows best.