Welcome to health care Magic.
The cause of your brother in law's death could be gastric perforation secondary to a gastric ulcer or esophageal varices
or esophageal tear.
As you have not mentioned anything about his health status or his addictions like has he had jaundice
or ulcer problem or he was chronic alcohol.
As far the bleeding due to gastric perforation is concerned, the bleeding is so heavy that the person often vomits large volume of blood.
As you have not mentioned about his previous health status, i can not say whther he died of perforation or not. But as far as your query is concerned ,yes large amount of blood will be vomited in case of perforation.
Hope you got my point.