How would you react to this situation?

So my dad, whom i haven't seen in 5 years, is coming back to visit us (divorced parents) and turns out he's married again and i have a step sister. We're all going to spend a few days in a hotel, all of us, my dad, my step mom and sister, my biological brother, and my grandparents. I honestly dont know wat reaction to have here. What would u do in this situation? What if i dont like them?