This is a tough one to track down details on. I apologize for the delay. Twins themselves are very magical and twins and the mother of twins confer fertility on certain crops in some cultures. Where in others they are considered uncanny and bad luck (probably in cultures where food and safety are scarce).
However, I did figure out a few things that might help.
A fig tree saved the divine twins Romulus and Remus (founders of Rome) by catching them in its roots. Fig tree roots would be a good component for your spell. Another European tradition is to roll around (with your partner perhaps under a full moon?) under a fruit tree to conceive, if you did this under a fig tree it may double your conception.
I understand your pov. And the subject of abuse should still be a major topic. And its not currently—online. But I can tell you, in the in person pagan circles I move in we discuss it regularly still. No doubt it will be heavily addressed during pantheacon one if the nexuses for pagan exchange and a convention KK spoke at and performed at this year on fairytale magic.
I think the specifics on KK had been dropped because of jerks harassment towards victims who spoke out. Until there is sentencing we likely won’t hear much on him. But this discussion continues in the background and changes must be made. Pagan gatherings need to be made safe for everyone.
I am gonna give you a few links from myself and other tumblr users, as well as to a lecture by one of my teachers.
Here is my master post on the subject: http://spiritscraft.tumblr.com/post/87214809182/the-other-and-sorcery
and another shorter one: http://spiritscraft.tumblr.com/post/70521351641/familiar-spirit-attraction
Here is a lecture by my teacher on it: http://www.heritagewitchcraft.com/apps/podcast/podcast/from_sidebar/2012/9
Ioqayin is a dear friend of mine and we are both students of the same tradition writes a lot on this subject, here are some posts: