I don’t know why everyone insists on calling the Vanir fertility deities, they not only have very few children, but the entire family has issues with relationships:
Freyja loses her husband somehow and wanders around searching for him.
Freyr can’t even court his own wife, he needs to send someone else to do it, and then said someone coerces her into marrying Freyr.
Skadi only gets to choose her husband by looking at his feet and then she and Njord separate.
Njord’s previous marriage with his sister was presumably annulled.
If you accept that Njord’s sister-wife was Nerthus that essentially means that all four named Vanir screwed up in the relationship department.
I mean are these really the deities you want blessing your marriages and kids and whatnot because I can name several other deities in committed loving relationships who would probably be a better fit.
PS. I love these deities they’re just the worst fertility deities.