after hours and hours of playing I think it might be impossible to get the poly route at this time I've tried pretty much every configuration of choices (romanced/non-romance Virion and Argandea as well as having both be my child's dad and making the choices that encourage their interest in each other) in different playthroughs and still haven;t gotten the poly route. I did finally get the options for either of them at the end after 3 or 4 playthroughs but could only choose one or the other.
Hope this makes sense!!!!
I will be trying more choices and will update if I am able to get the poly-route