It took my clowns almost 6 months before they figured out they had an anemone. Whenever I would see a tank with an anemone and clowns hosting it, I would get so envious. I remember I even printed out a pic of a clown in an anemone and posted it on the tank so they could see it. I don't know if it helped or not because they didn't seem to leave the hammer coral or mushrooms they loved hosting. Then one day, out of the blue, the male decided to sleep in the anemone. The female would continue to sleep in the mushrooms. After a few months, she decided she would join the male in the anemone. Now, they protect that anemone like I've never seen. Always chasing anything that gets close to it.
How long have the clowns been around the RBTA? They may just need some time, they'll figure it out eventually.