vft's don't have an extenisve root system so the depth of the pot is only important for the amount of water it can hold, but a wide pot could do the same. (however don't go too shallow, allow them to have some room)
4.5inch is about 9cm I'm guessing, you could easily plant more than 3 plants in there, You could crowd the place, the vft's will adapt to the situation. They will grow taller or make more leaves on one side of the plant where it recieves more light. Seriously 3 plants for a 9cm pot is nothing, I've seen pots way more crowded than that, go for the 5 or 6 plants you aimed for or even more. Depending on how big your plants are, you can put in more
Long term they'd be better off with more space (because they will divide and such crowding the place even more), but they'll survive.
Good luck