They get large and quick...I think they max out at 14 inches, mine grew from petsmart small size(2-3 inch) to the size of my hand in half a year. They are more aggressive in feeding than any of my cichlids.
I have noticed they are aggressive feeders. The guy at the LFS said they would make good tank mates for my school of 9 Odessa Barbs, but he was also wrong about what they were entirely so I have my doubts now...
those fish look like leptobarbus hoeveinni--- common name cigar shark or golden shark. They will max out around 20 inches. They are not tinfoil barbs because they are to streamlined. Had both a few years back.
I have three, each around a foot long. One of them is 12 years old (got it in 2000) and they are great fish. They do best in groups so you're doing it right. They eat most plants so you won't be able to keep very many in your tank with them. Also be ready for a big tank. I have mine in a 210 gallon tank with a few other fish.