Hello, I seem to have some struggle with finding the correct answers for the Freya and Synthia scene. Could I get some help?
Maybe you are referring to the one with Selphie and Synthia? There isn't currently one with Freya and Synthia.
In order to unlock scenes with Synthia, you need to have Freya breed you during her scene.
If you have scenes unlocked with Synthia, to unlock the dual scene with Selphie refuse to carry Synthia's heir. It's the last dialogue option during her normal scene where you also refuse to kiss her.