If you want to enjoy two clowns interacting I suggest getting a 20 gallon or 30 if you can and choosing percula or occelaris clowns. As clowns age they get increasingly aggressive. Four clowns would also make too much waste for a normal 10 gallon aquarium. If you can only get a 10 gallon stick to one clown, two will likely end with one large female dominating the other smaller male incessantly