Meeting half-siblings ...

I have an interesting moral conundrum I'm trying to sort out, and I'm hoping I might get some helpful advice from people on these forums. Firstly, some background. My name's Steve, and I was born in 1972. I was adopted to a loving family, and they adopted a girl in 1974 (unfortunately we never really got on). My adopted parents received a letter from my birth mother asking to meet me ... she wrote to them as she didn't know if I knew about being adopted. I met her and my "new" half-sister on Mother's Day 1999. At first the idea of finding my birth father hadn't occurred to me, but 2002 was a milestone year for me, turning 30 and getting married, so I thought I'd find him. He and my birth mother still had mutual friends, so she contacted him and arranged for us to meet. I met him and we had a good chat about various things, and he mentioned he had 3 other children. The freaky thing for me is, his eldest son is just 3 weeks older than me! He was a "busy boy", as my wife put it. I asked about meeting my other siblings, he said he'd talk to his wife (mother of all three), but the last time I heard from him was a phone message on my 30th birthday. I had decided to let sleeping dogs lie, until I joined Facebook and did some searching, and a few months ago I found my other half-siblings, I've confirmed this with various info on their sites. My conundrum is this ... my birth father wasn't too keen on helping me when I asked him, but here I am just a few mouse clicks away from my half-siblings. Would it be right for me to contact them directly and introduce myself to them? I have drafted a letter which I would send to each of them, but I don't know if I should. Any advice you might have would be greatly appreciated! Thanks for your time! Steve.