A question you hear often if you talk about India to a foreigner!!!!!
There is a solution.The family can add a disclaimer each time they use the Gandhi surname-Not related to Mahatma.
Feroze Gandhi was alive till a few decades ago.He was a Parliamentarian and had good credentials.So it won't be impossible to get details about his surname before he married Indira Gandhi in the 1940s,I guess.Can Right to Information facility be used.To my knowledge he was a Parsee man,atleast his father.Don't know if they have Gandhi as surname.Maybe some oldtimers can help settle this Gandhi-Ganddi-Khan issue forever.There would have been newspaper reports when Indira got married and some people would have saved them.Even newpaper offices can enlighten us.