aggressive behaviour

hi i am a mom of two boys elder one is 7 and the younger one is 5. my elder one is ok and he listens what ever i say to him. but my younger one doesnt listen to me any more. and all the time he is fighting with me and he has an answer of every question. ( he argues with me) and he keeps on repeating this thing that iam  a good boy even he does the wrong thing and he never  says that i have done wrong or he never realizes that he has done something wrong. instead of saying sorry or appolojizing he keeps on saying that ihavent done anything wrong and i am a good boy even i havent said to him that he is not  a good boy. and if i say that ia m going to punish u then he says about his elder brother that no u have to punish the elder brother even if the elder one has no concerns about the issues. though the elder one loves him very much .while playing the elder one makes the compromises about everything .
he was not like that before but he is becoming more aggressive nowadys. i dont know wat s the matter with him. and when he is in a good mood i tell him that i love him so much not only i but every one at home loves him so much.
the other day i told both of them to put on their shoes because they had to go some where but the younger one was hurting the elder one and he gave the reason that he is doing this to his bro because he listened to me.

even if we go to some where he doesnt litens in front of any one. what should i do please help me.?
really waiting for ur answer. so that he may get settle down with his agression as soon as possible  i think the earliear he will be able to control his agression and the better it would be for him.
looking forward for u help