Here I go again you can put a clown in a 10 gallon tank if you are willing watch it be unhappy and end up living a very short lifespan. There is a LFS
that is proof that a clown can live years and years one of theirs passed away after over 20 years and their other one is even older. They should be able to have a long and happy life in a tank that will suit their needs.
When I said anemone you can get something like a mini anemone or maybe one maxi mini anemone in a 10 gallon tank. If you do get one of those remember they do eat fish so take that into consideration. My rock anemone would be to big for a 10 gallon tank and it is still growing.