I don’t think so. If you see online, almost every image of a double barrel cake is of two tier; one small and the other one is big which is at the base. Also, if you deck up all the three tiers together, it won’t appear attractive. Filling is not a problem, you can use butter cream. As far as supports are concerned, if you take the cake barrels in three different sizes, there is no need for any support as such. Give it a try! :)
