Personally, I'm not convinced that Samuel was the father of Sarah and twin Alice.
Me neither. He would either have married her sooner not 4 years later or disappeared soon after she got pregnant if he didn't want to be a willing father.
Couldn't there be links to other possible fathers out there somewhere
I don't think so either, but perhaps he was more mature and willing to take responsibility at 25 than he was at 20. Against that, he didn't acknowledge her.
There could be some other father out there but 3 years of chasing DNA matches on Ancestry hasn't uncovered him - most matches turn to be from other branches on my mother's side, like Hancox. There then remains the problem of how I am descended from those Manton and Gaydon matches.