First, Trinity, my condolences on your brother's passing.  Losing a loved one is so difficult.
I also believe that our family and loved ones who pass on do return to visit us in dreams.  I've had very vivid dreams of my grandmother, my father, even a grandfather that I never met.  I think this is their way of comforting us and just checking in.
As for just dreaming of him only twice, I was a little puzzled over this too since losing my father.  We were very close, and I couldn't figure out why I didn't have these dreams of him more often; I would even try to will myself to dream of him.  Then, it dawned on me that maybe it was because he was surrounded by a lot of people who loved him as dearly as I did, in the afterlife.  In fact, in one of my dreams of him, he was sitting around a large table, enjoying the company of several people.  Some I recognized from pictures or descriptions, others, I didn't.  I'm pretty sure he's been busy catching up on old times with some of his loved ones on that side. 
I look forward to my dreams of him and other loved ones. I think these are little messages they send to us, or maybe just to let us know they are still around, and a part of our lives. Enjoy your dreams of your brother, I'm sure he has visited you to give you some comfort and let  you know of his well-being.