They're completely different animals, lol! They feed differently, swim differently, interact differently. . .
Do you know off-hand what the Gh of the water in this tank is?
Rams like their water soft and acidic, while Endler's prefer their water to be on the harder side of things. You may find it difficult to feed the rams in this setup without overfeeding the Endlers - assuming they're much like guppies and other live-bearers in their feeding habits - and either way, your beautiful Endlers would be uncomfortable in soft water, and your rams won't do very well if your water is hard. I'm not sure about Barbs, as I've never kept them.
If I were you I'd start with only one, and see how it goes - unless you are able to find a mated pair. You won't have the space to keep six in a tank that size - even if they play nice together - I think that there isn't enough room for them to choose territories, and overstocking can cause issues with tank parameters and rising nitrates, which the Rams may not tolerate. Then consider that re-homing them or separating them should they prove agressive toward one-another may be difficult. Its nearly impossible to sex a Bolivian Ram
as a juvie, and if you happen to get all or mostly males, you may find yourself in a world of trouble! Generally, these fish are considered to be semi-aggressive, and in my experience, they tend to limit their aggression toward others of their kind - meaning that they won't go after other types of fish. With that said, they *can* be very nasty toward other Bolivians, even unto death at times. . . Even if you are able to find a mated pair, be sure to watch them very closely, as I have read of several incidents where even a mating pair decide, for whatever reason, to 'divorce' and it usually ends badly for one of them, if they are not removed from the tank. They can also be aggressive toward other speceis if they're actively guarding eggs, so something else to consider.
Bolivian Rams are my favorites, I don't want to scare you away from the possibility of keeping them - as I'm convinced that you'd find them to be as fascinating as I do - but do your research here. They tend to stress easily, and aren't as tough as some people make them out to be, surely not as tough as Endler's or Barbs. I personally don't consider them to be a 'mean' fish, mine live in perfect harmony with nothing more than 'friendly' displays of dominance now that they've figured out their pecking order and have established their territories. But I've seen some instances in other people's tanks where things got bad quickly, so you have to be prepared for the possibility, and ready to move should any bullying occur.
ETA: I currently have four - three females and one male - in a 29 gallon well planted soft-water tank with very low nitrates. I would not add any more to my tank, and there are some who would consider even this to be overstocked (I don't, but each tank is different). I also have a 20 gallon long, and if I was planning to stock rams in a tank this size, I'd put 3 at the MAX - but I've never done it, so this is just a guess based on my own limited experience with the species. If you DO choose to get more than one (and I must again recommend that you start with one, and only IF your water is right for them - just to see how he/she does in your community) I would say to make sure that there is only one male in the group - or even stick with all females. But again - this is really tough to tell when they're juvies, and only slightly easier as they reach adulthood.