there are some things about demons and terra prime that came up in the demons baby thread and since it is hard to answer with out going into what may be considered shippy stuff..
about why trip was the father..
we do know just like soong for some reason paxton did know about trip and tpol. he even calls them "star crossed lovers " to trip in demon.
also take into consideration if they had access to the dna they also possibly had access to phlox medical logs which contained info about lorian . which means they might have had some guideline in how to create a child from his sensor readings ect.