if you want girls in the same tank and have the opportunity to get some who are already stocked in the same tank, I would get them. Now i'm not saying that the girls in the plastic cups won't work, because that isn't necessarily the case. This is a situation which largely has to be played by ear. I have a very large girl and a very small girl sharing a divided 2.5g until I can get my sorority tank put together and cycled. The little one is from a LFS, the big one from a good breeder, but they still get along at least long enough in neutral territory that i can change the water in the tank without fussing over what to do with them too much.
If you can't get a second tank, make sure you add all the girls at one time OR you rearrange the tank whenever a new one is added. This way no one female will already have an established territory that is unknown to the new fish. However they will still probably fight so make sure you have some medicine on your hands for torn fins and plenty of plants and caves for them to get away from one another in. The tetras will enjoy a well planted tank as well. In most cases I've heard, they settle down within a week or two, but keep an eye on them. If one is especially aggressive after most of the hierarchy fights have ended, or is looking unwell, remove her immediately. A gallon bowl or tank will be sufficient for her. Unfortunately removing a fish may cause them to start fighting again to reset the hierarchy.
I don't think I've really missed anything, but if i have, other forum members should be able to cover it. There are plenty here who know more than me, and who have experience with sorority tanks (I'm only repeating mostly what I have read on this forum in the past). Good luck, i hope it works out
-miriam
one last note, I don't know if this is necessary, but it might be wise to ask for seperate bags for each fish if you DO get them from the store that stocks the girls together. They may do this anyway, but i wouldn't want to see a fish die between the stress of being shipped, as well as being confined in so small an area with five otherstressed and unhappy girls.