Well yes, this was revealed in "the variable". This would make Daniel and Penny half siblings, Daniel being Penny's half brother, and Penny being Daniels half sister, though each of them are unaware of this fact currently....
posted over a year ago
Wouldn't it make them half-siblings if they both have the same father?
well Widmore said "he's my son too". So i guess Daniel and Penny are at least half brothers/sisters. One parent in common. Unless of course Eloise is also Penny's mom.
Daniel was the son of Eloise Hawking and Charles Widmore, although he did not know the identity of his father. He was a very gifted scientist, but enjoyed music more.So Daniel and Penny are siblings,neither of them know that.