Monkey D. Garp
Monkey D. Dragon
Monkey D. Garp
Portegas D. Ace
Monkey is the same for Garp, Dragon and Luffy, and Portegas for Ace.
So Luffy's grandpa has same last name as his father, the same as Luffy, and Ace has different.
And the wiki, what ground do it have for stating that...