They may feel a bit lost in such a big tank but they should grow into it quickly. I would actually suggest adding some things in the tank to help them feel comfortable in such a large space. Make sure any wood you use is sterilized. I would be careful of cross contamination of using plants, and absolutely would not recommend other fish for the same reason. It sounds like this is your first discus tank and adding either of those adds complexity that you don't want when you first start with discus. After a few months when you feel comfortable you could look into adding other things with proper QT protocol.