Bio-dad Denies he is Bio-dad...now what?

I am 47, always known I was adopted..raised by 2 beautiful parents with 2 siblings (also adopted from other bio-parents). About a year ago, I found my Bio-mom. We have emailed several times, and are waiting for the right time to actually talk...she travels a lot, and has been a little anxious about that, which I have been respectful of that. (her fairly new husband also in unaware of me, so I am also trying to be understanding of that) She gave me the name of my Bio-dad, which i was able to find and contact. He was doubtful we were related, but agreed to meet with me..as we live about 90 minutes apart We had a decent meeting, however, he doubts he is the father, implying Bio-mom was probably having numerous encounters, and he was the best candidate. (he was a 2nd Lieutenant in the AF). She was a single mom with 4 other kids at the time I was conceived. She tried to contact him and his CO at the time, but she never got a response. She then arranged an adoption. I told him she was **** near, if not 100% positive he was the father, as she was not involved with anyone else. He has also has a son, that also lives about an hour from me, and is 5 years younger than me....which means i may have a half brother. I would like to contact him, but thought i should advise Bio-dad of my interest in meeting bio-brother. He was not happy about that..again denying me he is Bio Dad, and stated he would prefer me not to contact his son (already found him on Facebook), and to not contact him anymore. I had suggested a DNA test when we met, but he was not interested. How hard should I push for a DNA Test? If he refuses..again....should I approach his son? Any advise would be appreciated.