Shalom ( Scialom) Carlo Gattegno - Father

Baruch Nahon does this mean he didn't perish in the Holocaust, but died on Rhodos?

https://www.jewishencyclopedia.com/articles/6528-gatigno

could he be Abraham?

Yes, Shalom's death in the shoa is one of those viral mistakes that happen in online trees so often... Other than in my tree (on myheritage) you will not find a correct one (at least, I couldn't). It can be checked on Rhodes cemetery website or the testimonies in Yad Vashem or the Fondazione Centro di Documentazione Ebraica Contemporanea where there's even a recorded interview with her daughter where she explains this.

I have a few Abraham / Albert Gattegno / Gatenio in my tree but no data that allows me to link him with a son named Shalom. Even having a father named Shalom would be a hint, if the Shalom grandson is the bechor...