I find it interesting that Peter states that he believes his two other siblings were merely sent away, yet phrases it at the beginning as "two of my sisters still live." I think he strongly suspects the other two died, but chooses to believe otherwise.

Yeah, that’s a good observation! Honestly, he spends the first half of his statement trying to make excuses for his godawful childhood, so it tracks that he would reach for the least horrific explanation for what happened to his siblings. He acknowledges that he went through horrific shit and then is like ‘BUT IT WASN’T THAT BAD THO’.