One of those questions that I don’t think has a definitive answer.... I have 5 together in a 180 that have been together about 4 years, all added together pretty small in size... all live happily together within a very large Mag Anemone so I don’t think tank size plays a part at all.... As expected one has grown larger than the rest.....In a nano I probably wouldn’t risk more than two together as a precaution but I wouldn’t want to say it can or can’t work for sure
If you were determined to and had time to oversee the tank a lot, I would add 3 of the same size and be prepared to remove one if necessary. My only rule for multiple clowns is to keep the numbers odd so as to avoid multiple pairs. Multiple pairs probably won’t end well.