Luffy's father is Dragon (world's most wanted criminal) and grandfather is Garp (marine vice-admiral). He has a brother named 'Ace D. Portgas' from the same father but different mother. Does Luffy has a sister?
Shichibukai has been mentioned in the manga several times as the 7 strongest pirates of the world. This is arguable. Luffy has defeated Crocodile and Gecko Moria out of some luck with the help of water and 100 shadows. Nevertheless, we had seen powerful figures such as Barthelomew Kuma who seems to be very formidable because of his teleporting power and Mihawk who can cut through logia-type devil fruit users.
Tom who is/was the master of franky and iceberg might not have died. The marine might have put him away for good in level 6 of impel down.
There are still some unexplained foreshadowing scenarios in the past episodes. One of it I could think of is why the marine did not use the real photo of Sanji in the wanted poster instead of using drawing. The marine officer seemed to be shocked when the photographer presented Sanji's photo to him and he wanted to keep it a secret.