Reuven Hassan - Reuven/ Rezso

I think that Reuven is another brother,
because his date of birth is different then Rudolf/Rezső's.

No. We have two funeral notices for Rezső and the birth dates differ by, from memory, 4-5 years. Clearly one was a misprint

According to the Historical Archive of Sombor, Reuvan Hassan was born on 20/3/1859,
as I wrote in his profile.

Interesting. Hasán Rezso’s obituary says he died 10 January 1898 in his 40th year.
So either Reuven was a brother, possibly a twin, who died young, or it’s an alternative name.
I haven’t seen the name anywhere else in family archives.
However, Nina Hassan’s obituary does mention grandchildren, Zorka and Regia Hassan, and I don’t know who their parents could be

I hope we'll be able to find out.