Maybe it's a 6yo thing. My dd went through that when she turned 6. It about drove us nuts. She would do something and turn around, look us straight in the eye, and lie about it! We finally had to get strict with her on this and really break it. First, we had to come up with a consequence that would bother her. She loves the computer so we took that away for a day each time she lied. That helped. Then, we hit it where it really hurt. We took her bike : ) I also had a long talk with her. I talked to her about how if she had just admitted to doing whatever, she would have been in trouble for only doing whatever. Now she's in trouble for doing whatever and lieing. She was able to understand that. She just turned 7 a few weeks ago and I didn't realize until I read this that she had stopped with the lieing (or she's getting better, ha ha).
As far as making up stories like his sister, he may just be actually storytelling. Maybe he heard a story or watched a tv show about a 10 year old sister. When he does this, I wouldn't give him a consequence. I would maybe ask something like, "Is this really true or is it just a made up story?" Just make sure he learns the difference between when it's ok to tell stories and lie about something he has done. My kids and I even pass time by making up stories.
As far as listening, my ds can be like that. I can tell him something and he's "uh-huh" and I know he didn't pay attention. What helps with him is to stop him and ask him to repeat what I just said. I also have to take away distractions. If we're getting ready to leave and he has to get dressed and put his shoes on, it will not be done if the tv is on. So I turn it off and have actually told him to focus on me, lol. It works. Or if he's playing with a toy, I have him put it down and look me in the eye when I tell him to do something.
L.