The big mistske.
Emily was so scared of losing her hasbund she told her mom hoping find a solution to their problem and yes they found it.
Well in this town was a very big witcher he was so scary and no body can get over him , but they had no choice , they went to him and told the whole story and that's what he says
"I'm going to let you have twins but you are going to pay something in return if it's not today then you will face it in the future. Because this a black magic a dangerous one, it's true that he will save you from your worries but on the other hand you will have a huge price that you will definitely pay it."
Of course Emily doesn't doesn't pay attention of what he said at the end she was so excited and happy so she accepted the offer.