He's in 1st grade, far too young to overthrow you as head-of-household! He needs to realize that to be independent he also has to behave positively, not negatively as he has been. And since he's "sensitive" he especially needs not to be coddled or his behavior will get worse.
1) Set a timer for the amount of time you will tolerate his venting. Once that time is over it's time for him to move on to other topics, even if you have to remind and redirect him. Tell him complaining and whining are over for the day. If he wants to continue after that say something like, "I really am sorry you had such a horrible day. It sounds like you need a nap." And send him to his room to lay in bed for 30 minutes, not play. If he's OK after that amount of time he can come out, but if he's still grumpy he stays in there another 30 minutes.
2) Make dinner and if he doesn't like it he may be excused, you don't listen to his complaining (it's rude and disrespectful) AND he doesn't get anything else to eat (but of course he can have his dinner food if he gets hungry.) Before he goes to bed have a talk with him and tell him that he needs to eat the food you prepare him, not be rude and complain about it, and that you expect better behavior out of him.
Also have him help in at least a small way in preparing the meal; rinsing the veggies before you cut them, pouring milk, setting the table, etc., if he has a hand in preparing it he may have a different attitude about it. Also give him a choice in the meal, something you already considered such as, "Should I make green beans or carrots, serve fresh fruit or applesauce, etc?" then let everyone know he made the choice in selecting whichever.
3) Have him set out his clothes the night before, after his bath, before bed. Tell him what he'll need, shirt, pants, socks, jacket or hoodie, etc., and have him pick it and lay it out. If he has any complaints the next day kindly remind him HE picked the outfit out.
4) Tell him the school year has a looooong way to go, and that he will more than likely be receiving an award at a different time. (Teachers do try to make sure every student receives an award at some point throughout the year.) Tell him he should be happy for other children when they get an award and he doesn't, he would want them to be happy for him, wouldn't he? Tell him to make sure he claps for them to let them know they did a good job. Also tell him we don't get awards because we want them, we get them because we did something to earn them, and the teacher can't give him one until he does what he's supposed to do without being grumpy about it.
5) Life ISN'T fair, and never will be. i won't go into how unfair it was to the thousands of people who died 10 years ago tomorrow. Or the children who get horribly sick with cancer at very young ages. You get where I'm coming from. Life isn't fair, agree with him on that, and tell him since he knows it isn't he shouldn't expect it to be. The best he can do is deal with life as it comes to him and make the best our of it. (Lemons into lemonade, so to speak.) When he starts to whine and complain on how unfair life is have him sit and write down 3 things that are good in his life. Do it each and every time he complains about something and he just may stop complaining (unless he likes writing.)
6) Tell him his brother and sister are so fortunate to have him as a big brother, I'll bet his sister is "bugging" him because she wants to be with him or he has something she thinks is cool and wants to play with it, too. Tell him yelling at her isn't nice and hurts her feelings, and he knows how that feels. Does he want her to feel the same way? She loves him, he should love her back.
It sounds as if he needs to stop focusing so much on himself and think of others. TV portrays lots of things in distorted ways that make kids think that's the way life is supposed to be. I'd wean him off TV, and only allow him to watch when the entire family is watching something together. That way if he starts to get negative ideas you can head them off by simply changing the channel or turning the TV off. Maybe Family Game Night or reading would be better activities for him to pursue. Here's some food for thought on how TV affects our children:
http://kidshealth.org/parent/positive/family/tv_affects_c...#
And since he's in 1st grade it may be time to get him into a sport with other kids his age. He'll get a bigger perspective of the world and learn to pursue things as a group rather than alone selfishly.
Try to nip the behavior now or you will have one moody child on your hands in years to come. {{HUGS}}