Good answer from Will about the tamarins. Other potential species to base your creature on are:
- Vervet monkeys. Here's the wikipedia entry. Vervets have a 'proto-language' as they have different alarm calls for different predators, since the response should be different. They also do very, very basic tool use
- Capuchin monkeys (various species) are tool users with much more adept and sophisticated planning than the vervets, as this BBC clip shows. They also and have proto-language alarm calls. This video clip at about 4 mins 50 seconds in shows a sequence about a capuchin being cleverly deceitful.
For castes, you need to have division of labour. A 'queen' is reasonably easy - you have a dominant female who produces all the young. Lots of mammals (mostly pack-living canines like wolves or African wild dogs, but also mongooses and meerkats) already do this: the alpha female harasses the subordinate females physically and emits pheromones in her scent to prevent them breeding. If they do breed, she often kills their pups. Her own youngsters stick around to help her raise the next litter: This is called cooperative breeding.
Your creatures (and mole rats or ants) have taken the next step, and divided up other tasks, not just the breeding. In the case of ants, the castes are fixed - you are a soldier ant at the beginning, middle and end of your adult life. You have a body tailored to being a soldier ant (e.g. big jaws and/or a powerful sting). In the mole rats, however, caste is more about body size: when you are little you dig tunnels, when you are big, you defend the warren.
If the ancestors of your creatures have fungus gardens in a nest (like leaf-cutter ants do) and helpless babies which can't travel with the adults (like ants and mole rats do), they therefore have a fixed home to defend. That would have encouraged the evolution of a 'troop' or 'colony' to defend the queen's offspring and food supply. Which could eventually lead to true eusociality.
If you want castes as bizarre as honeypots in ants, you'll need to invent the 'job' they are doing and the biology or ecology to justify it (crippling food shortages at certain times of year for the honeypots - leaf cutters solve this by fungus gardens instead of honeypots).