Hi Charles and welcome to SimplyDiscus. These guys do not seem to be behind in their growth but since you are a newbie it would really be best to grow them out in a bare bottom tank for best growth and health of the fish. Since some of the plants are attached to the wood you could pot any plants needing to grow in the substrate and remove the substrate.
You will be shocked how quickly the substrate will collect junk especially once you start feeding the BH mix. That junk can really affect the health of the discus. If you decide to remove the substrate please post so we can suggest to good approach for substrate removal.
If you poke around the forum you with also find that discus do better in groups of six or more. This is a great place to learn about discus and the fish are well worth your time and effort. Here's a thread in the beginner section of the forum with a great video on keeping discus
http://forum.simplydiscus.com/showth...CH-THIS-VIDEO!. It is an hour long but well worth your time.
Pat