Did Geralt get Yennefer pregnant?
No, Geralt didn't even meet Pavetta until she was already pregnant with Ciri. Also, as a Witcher, Geralt is sterile, so
he can't get anyone pregnant. , played all of the games, read all of the books and stories.
Who killed Ciri's mother?
In fact, Vilgefortz had been conspiring with Duny to bring both
Pavetta and Ciri to Nilfgaard. Pavetta ultimately figured out Duny's plans and arranged to leave Ciri behind with her grandmother, much to Duny's ire. The two then argued and she fell overboard and drowned.