Given Sienna's conversation with Dodger I think she genuinely doesn't know who/where Nico's dad is as she told Dodger she slept with a boy she hardly knew and Patrick made her feel ashamed of this.

Then I really don't understand why they've been so overly dramatic about this. We had a line from Patrick awhile ago that if Nico and Sienna were ever reunited and the truth came out "it would destroy the whole family".

The whole family? Who would that be, then?

Maybe he meant the truth about him keeping her locked up in a cellar for months on end, forcing her to give birth on her own without making a noise, and then selling or giving away the baby and telling her she had died.

Since both Sienna and Patrick are inveterate liars, it's hard to know what the truth is.

I genuinely do think Patrick is the father.