While it is short, this dream provides much to think about. It can be examined from a number of possible viewpoints. First, it is important to note your feeling when you awoke that the dream was very real. This might mean that it will happen, that it happened already (in another lifetime) or that it has the potential to happen symbolically, which is the most likely scenario, unless you are the kind of person who often has dreams that predict the future.
If we look at the dream symbolically, it may represent your feelings towards people in your family and yourself. Note where you are standing at the start of the dream--not in the house, or on the back porch, but away from the house, looking in toward the back porch door-- signifying possibly that you feel quite distant from the family and that you are ready to be in a transition concerning your family relationships.
Your sister-in-law, on one side of the door, might represent your feelings about your relationship or marriage if you are in one, or hers (if you are not) and the other person, on the other side, may represent a desire for something new, or different in your relationship or marriage, or for a change in your relationship status. Your uncertainty about whether the person was male or female might represent some uncertainty in yourself about your sexual preferences (or those of your sister-in-law)--, especially because you did not say "man or woman" but "male or female"-- the words we use in describing our dreams are usually quite significant--or it might just mean that you are feeling uncertain about who to turn to for closeness--a male friend or a female friend.
The "male" who was having an argument with your sister-in-law was standing "straight" out from her--again having to do, possibly, with sexual inclination--which may mean that you have some doubts about the sexual orientation of a male person in your family and your uncertainty about his age also shows that you there may be more than one male person in your family about whom you are concerned in general--one old, and one young.
That your brother, W., came out the back door to see what was "going on" shows a possible concern you have that W. may be "coming out the back door" or not really aware of what is happening in his own family, especially regarding his wife. The male pulling a gun and shooting him in the head, killing him, could be someone who has angry, violent feelings toward him, or someone who wants him "dead" or "gone" in terms of the family, or his marriage. Guns also have sexual connotations. It could also represent a manifestation of your fears for your brother and his marriage. You screamed and ran to him, but he was dead, which shows that you would like to help your brother, but feel that you are powerless to do so.
Whether this dream represents a real scenario that will occur, or a scenario that will occur symbolically, or your feelings and fears, is something that you must determine. If you are unable to do so on your own, you might seek out the services of a therapist or counselor in your community. I do recommend taking stock of your feelings about your family--especially your brother and sister-in-law, and your own relationship or marriage (if you are in one), and talking with family members about your concerns.
Dreams can be helpful in making us aware of feelings and concerns that are buried deep inside. If we pay attention to them, we can learn and grow. It's easy to say, oh that was just a weird dream, but usually we can gain insight from dreams that seem quite strange.
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