What do you mean by 'live barriers'?
What kind of killies did you see? There's a huge number of species and some are more suitable than others. Many are actualy not worth keeping in such a large tank as they are much more interesting to keep as pairs in a small tank set up to allow them to breed. Others need exceptionaly peaceful tankmates while others have a very short lifespan or special requirements. Though there are lots of itneresting species, the only one I've realy enjoyed keeping and have experience with is the American-flag fish which looks somewhat like a multi-colored platy with cichlid/gourami behaviour that I've always found apealing. It is not your typical killi though...
Anyway, if your brother wants to try a peaceful community the options are truly endless.
If he'd like that sort of thing, he could try a heavily planted tank with very small species: 6-8 spotted rasbora or neons, 3-5 sparkling gouramies or 3-5 mosquito fish (heterandria formosa - not gambusia affinis which is aggressive/nippy) or 3-5 endler's livebearers or 3-5 guppies (make sure not to mix endler's with guppies as they'll hybridize and either keep the above at a ratio of 2 females for every male or go for a single-sex group), 4-6 pygmy cories and 3 honey gouramies (colisa chuna/sota - not colisa lalia which is slightly larger and much more sensitive).
Alternatively, he could try a tank with lots of color: 5 dwarf neon rainbowfish/praecox rainbowfish, 3 kuhlie loaches and an opaline gourami OR a trio of platies/swordtails if he preffers.
Or maybe he wants a 'typical' peaceful and well-balanced community in which case I'd go for: pair of pearl gouramies, 5-6 harlequin rasboras (or 5-6 black phantom tetras) and 4 cories (I reccomend either bronze or blackfin).
I'd probably also like to go for something that looks more out-of-the-ordinary but using common species: 5-6 hatchetfish of your choice (but nothing too small), 4 glass catfish and 2-3 kuhlie loaches. You'll want to feed the glass cats some live foods to keep them healthy and don't buy dyed ones.
He could always go for a shell-dweller cichlid tank or something like that...
The options realy are endless and I don't know what else to suggest
If there's a small-ish, relatively peaceful fish he'd like in particular he could use that to build around and choose suitable tankmates. Or go for a bio-tope set-up. Or choose a theme and go for fish that fit. Otherwise it's realy difficult to narrow things down. For example, I like gouramies so I almost always build my community tanks around a gourami species.
