not necessarily, its already established that Tom was a sperm donor in Sophias case, we dont know if it was a "custom donation" or if there are "donations on file" at a bank. there could be other sibs out there.
I might be misremembering but If I recall Liz kind of insinuated that Katie's dad was a good for nothing shitbag, which would lead me to believe that she knows who the father is. I could be wrong, but I don't get the feeling from what we know so far that his dad was a shitty person, so I feel like that's an incredibly long shot.
Again though, I might be misremembering and maybe Katie's dad was never referenced to even a bit, but for some reason I think I remember him at least once being brought up, and not in a good light.
So if I'm wrong, please just ignore this.
![Big grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)