@thegoatrider previous chapter as well as in the novel mentions how all witches are infertile. by gaining the ability to use magic, the witches become unable to give birth to a child.
Why so much problem, doesn't king usually have multiple wives? Just join the harem and find another one that can give roland the heir. With roland personality, he won't take a queen that can't live nicely with anna anyway
Heck, I don't even think roland would care about having heir. He might just pick some trusted person or child and train him to be the king