That's a fanmade WANTED poster, that's not real.
Anyway, here's my thoughts. Serious thoughts on Shanks being Ace's dad. I think It's true. That's why he cares so much about Ace. I mean, Garp freaking Hates Shanks. He abnormally hates Shanks.
And I don't think it's entirely because of Luffy being a pirate. I think Shanks got Garp's daughter pregnant and skipped town.
Ace has narcolypse. That's a Monkey D. Trait. And Dragon is not Ace's dad. Luffy and Ace have the same mother but not the same dad? Yeah, I do not think so. Dragon would not marry his Sister. That's incest!
Luffy and Ace are related by blood, but they're first cousins, which is close enough to half siblings. From what I see, they're calling each other brothers because of their closeness in age and growing up together on the same island.