If any wolfrider was going to have children with more than one mate, it would have been Rain. He could have controlled that, being a healer. It always seemed to me that Pike, in addition to being an experiment in being born outside of recognition, might also have had a different mother than Rainsong... or Shale, if Shale were Rain's son.
Bearclaw tells Cutter that a wolfrider's life is short and sharp- like a bolt of fire in the night. Why would he say that if his tribemates tended to live to a ripe old age? We know that several elves of the previous generation died off. Trueflight disappeared. Rillfisher died. Clearbrook's daughter (who we never met) also died. Rainsong and Pike's parents. Skywise's parents. Someone named "moss" who appeared in the BoTC books, but never in the comics. Etc.
And then there are the elves like Redlance and Foxfur, Brownberry, etc... who don't seem as old as Longreah, Treestump or Bearclaw- but perhaps around the same age as Strongbow... and they must have had parents who passed on.
I think Rain might have had multiple mates- at least a couple.