Put some ice on that

Maybe mom slept with more than one person?

Half-sister, step sister, their parents got divorced and the mom got his/her sister and the dad got him/her and the mom remarried. There are quite a few solutions.

"Blob" of ice? xD

Both my brothers and i have different fathers

Yeah, well my sister and brother have a different mother from me. My dad had them when he was married to her, he got divorced after hearing she was cheating, she married that guy and my father married my mom.