So Robin deserves to die because of what her mom did?
No one in Ohara was fomenting war within their own country by killing off all their political rivals.
Robin (and her mother) weren't benefiting by subjugating their local population.
The cockroaches from the Kurozumi clan were still intent on bringing down and subverting the Wano country through trechery, you can't say a lot of these people aren't evil, were there innocents that were unfairly killed? yes, would Orochi have been one of them if killed, arguably not, even at the age of 13.
Orochi was 13 when he got the fruit and would have lived a life filled with immense privilege from the ill gotten gains up until that point, he knew what his grandfather did and was mad that he was chased out of civilized society, he could have distanced himself from his grandfather, changed his name and reflected on the actions and worked for an honest life, instead he was an evil retard killing TRUE innocents.
Young Kanjuro I feel bad for, he didn't profit from the situation and wasn't a direct lineal descendant, he was a true innocent.