Rummy nose are extremely sensitive to water conditions, as well as good sized and quick. A 10 gallon is no where near big enough for a proper school of them, not to mention multies will chase them. These may be tiny fish, but if they had the size of many other of the larger tanganyikans, they'd be one of the more aggressive species. They're like chihuahuas of the fish world, a "little fish complex" if you will. Your bristlenos's fins will more than likely be shredded too, and may eventually be killed. I'd also switch the coconut out for Texas Holey rock. I wouldn't recommend a bnp be in a 10 anyway, and multies rarely use anything but shells, the reason being that they use the shells for protection from predators, and in a larger cave like that, many fish could get in or part way in and eat them or their fry.
As for grouping, make sure you get about 5-6 right off the bat together. Once they establish territories (usually an area with a diameter of about 4-5") they will beat and kill any new comers, even if there are open shells. These fish are highly territorial, especially the females and even more so when they have fry