well, I would still add more. It isn't that these two cannot be compatible and for sure won't bond. There is never a for sure answer to that question. They may bond and be a great pair, but they very well may kill each other as well. That is why festae are tough, they can be unpredictable. That is why when you have a large number and they can choose from many, you have a much higher chance. It is not a easy process that is for sure. So, in the end, the only thing you can do is raise your chances of getting a compatible pair by getting more juvies.