Some advice please!

Ashley • This is my first pregnancy at 29. I'm scared and overjoyed at the same time. Due date is November 24th, I'm now 5w and 3d. I was born November 26 so I'm hoping my baby will be born the same day
My sister and I have different dads. My sister recently told me, she's dating my brother on my dads side. Is that weird? It's sitting uneasy with me. I've explained to her in the past that I share blood with both of them and it would seem odd if they dated and began a relationship. Should I just let them be? Am I over thinking the situation!