My wife’s father did an ancestry dna test to find his half brother as well just a few years ago so my wife and I also did ours after what he discovered. When my results came back I was informed that four of my cousins on my dads side were actually half siblings. I give my dad crap about it all the time but thankfully my mom is cool with it. I guess when your dad is an identical twin all the kids on both sides show up as half siblings instead of cousins.