When do you know if you have a problem?

[tostaky]

...because we've been wondering...
It's really hard to tell if DS1 is within the norm or if there is something wrong with him. He is almost 4.
He has a very bad case of selective hearing at home, nursery and any sports groups he has tried (swim, football) - he just ignore people who are talking to him.
He plays with everybody at nursery but he is obsessed with one little boy in particular and that causes drama when said other boy, doesn't want to play with him
He is very bossy with his younger siblings and often make them do the things he knows are forbidden (eg. I've just told him to not bang a toy on a wall, so he asks DS2 to do it instead)
When I tell him off he turns around to DS2 and says "we are going to kill mummy" of course DS2 being so young says "ok!"
he is obsessed with pirates, guns, anything violent even though we do not have a tv, do not watch DVDs, no xbox and the likes, no iPhone etc... He has one book about pirate dinosaurs, nothing else about people being killed or violent... Must come from nursery. I am always here for playdates so i know for sure it doesn't come from his friends outside nursery either. Any outings in the woods and a stick become a sword or a gun... It is tiring...
Oh and he ne ever listens! Or do what he is told...
So have we got a problem?
Have we got a problem?

What kind of problem are you worried about? Lots of children have obsessions and talk about killing people, often they have no concept of what it means, they just know that the word 'kill' gets a horrified reaction from you. To them, that reaction is funny. It sounds to me like you have a very clever little boy who knows exactly how to get a reaction from you. He has picked up on the fact that you do not like violence and is enjoying the shock factor. There is a method of behaviour training that I use (I am a teacher) called ignore and praise. When your son elicits the type of behaviour that you do not like, you ignore it, but when he does something you do like you give lots of praise. In the example you have given above that would mean when he tells your younger child to bang something on the wall you ignore him and say to the younger child (in a happy tone) "you arent going to bang things on the wall are you? because you are a good boy" and then distract him with a game of some sort and give him lots of attention. Invite your older son to play the game too and then praise him to the hilt when he does anything that shows friendly behaviour. When he says things like 'we are going to kill mummy' ignore the comment and say something like 'who loves mummies special tickles?' and start to play with the younger child. Again, invite your older son to play and give him attention for positive things.
With the selective hearing, you might be able to correct this by praising him when he does listen well. If he starts to ignore people, get down to his level and say 'you need to listen carefully to mummy now' give him the instruction then ask him to repeat it. When he repeats it properly praise him. The idea behind the technique is to try and give genuine praise every time you see something positive. In the classroom praising a pupil who is working well often causes the pupil who is chatting to stop and get on with their work. However, telling a pupil off for chatting often results in a power struggle between the teacher and pupil because they feel embarrassed at being told off and try and save face. Praise is a brilliant tool if you use it often enough.
I hope this helps xx

Sounds completely normal to me.

Since you mention 'selective hearing' have you had his hearing levels checked. My ds's have hearing loss, and it can be quite deceptive. Ds2 can hear a whisper in a quiet room, but not a shout in a crowded area. It's an easy thing to get checked out.