Trying to write it in English in the most literal way as possible:
"The great age of piracy, since the moment its curtain was open, seek the seat of the pirate king."
The text itself is not literally saying anything about "those three", but considering just that text alone as its written under that image, then it's referring to Moria, Crocodile, and Mihawk; It's basically saying that since the beginning of the great age of piracy those three have been seeking the seat of the pirate king.
But well, if the whole page was about Crocodile, then it's more likely that the text was really just referring to Crocodile.