Mah, I'm not sure if they're all related. It gets confusing. I know Garp is Luffy and Ace's grandfather. Teach is...

[Long pause and you can practically hear the storm cloud on Marco's end before he speaks.] A traitor. He wants to be like Roger, but only in the sense he thinks he wants to be powerful. I guess when Roger was around, Teach didn't pay much attention to how the King really was. So related or not, I don't think they prefer to keep those connections.