"¿Tú tienes una abuela?"
Translation:Do you have a grandmother?
"Have you a grandmother" is a perfectly acceptable translation but DL says it is wrong.
But DL has only been making this mistake for the last five years. Have you a lot of patience?
I believe that duolingo uses American English, and in this case that would not be correct.
It is not, but when it is not used, "DO" is obligatory: "Do you have..." American English does not use the "have you..." construction.