As we've said before, Watership Down is kind of like a heist film where a group of people come together to pull off a big crime, and all of those people are necessary team members because each has their own skill. (If you prefer, let's call this the bunny A-Team.) Each of these rabbits has their own gift to bring to the group. So each of these rabbits helps Hazel's warren survive.
Dandelion tells stories, Blackberry invents, Pipkin … well, idolizes Hazel (which isn't actually all that useful, but it's something), Bluebell jokes and keeps spirits up (and also tells stories), and Blackavar, well, his skill is really his love of freedom and the example he sets by going through terrible pain to achieve that freedom.
Clover, Hyzenthlay, Vilthuril and the other does are the romantic interest in the book, though as we argue elsewhere, they do a lot of work as symbols (rather than as characters). There aren't a ton of feelings here—only an urge to breed more bunnies.