Without hesitation I'd make Parker Philip's son again. Clyde blackmailed Ian to change the results (yes, the all-powerful, all-purpose Clyde was involved in Salem years before anyone knew it) because Daniel bedded his wife and was the true father of the baby that died with her. Unbeknownst to Clyde, other agents were also changing the results, so it didn't go his way.
Teen Parker comes to town with Philip, the elder of whom intends to be a thorn in Xander's side but ends up being an asset to his brother. Teen Parker (turns out Parker, Kate, Chloe, Holly, and Philip learned about the paternity before Holly was SORAS'd and nobody mentioned it in Salem) is infatuated with Sydney.
Holly develops a crush on him while trying to make Tate jealous (don't worry - they learned the paternity truth in a backstory when they were still in jumpers) but he thinks it's too close for comfort since they almost had the same dad and were birthed by the same womb.