You can have both of them if you bind Xyless to you. Then there isn't any issue with your morality level.Oh well, do you recommend Carys or Xyless?
You can also use the editor to change your morality level before you talk with Xyless in the guest room after recruiting her to make it low enough for her to agree to be your consort, then after accepting you can change it back to what it was. There doesn't seem to be a morality check for Xyless after that point so she will stay and the check for Carys will pass so she doesn't leave. I have played many games where I have both of them in my party until the end.