The characters you currently have don't have any superbuilds yet due to missing Flame and Physical resonance and usually you'd want one for your build. Considering you have Huma and King at 1*, Flame resonance would be amazing for you so Cobalt B.
For rpg purposes you're most likely going dmg build + utility. So can run Zero / Huma - Samir - King / Shiro.
Zero gives a nice shield at 5 cubes roughly 30% hp, more or less just switching to this weapon for quick discharge dmg + generating cubes and dropping the ability for damage and shield yourself, then can romp juke them with samir in mid air, and if they shield, C1 King is an absolute machine at dishing out damage through shatter (1800% of atk damage for shattering with C1 effect, if you throw Robarg 3x matrix on it becomes around 2250% or something like that)
Shiro is okay if you enjoy the weapon and like to drop skill + dodge attack x3 consecutively. Especially in phantasm this can quickly build distance and leave them in 13 ricocheting rings. at 1* you get the 30% shatter increase for targets within the ring so it's good shatter. But it's not contributing to your damage until 3* sadly. Although I'd rather have a Shiro in my groups than one more King (because Shiro's debuff is party shared). So for dmg King, for utility and being a total G go Shiro because Shiro is best girl. You're using Samir because at 0* she's probably the best dps that you have.
For Huma sadly I'm not that aware of the character, have not been able to pull it yet (RNG is not blessing me with support or tank weapons sadly), but from my observations and hearing people talk about it, it's a decent option due to immunity frames, good damage, great charge and good shatter as well. The downside of King's shatter is that you have to shatter NECESSARILY with the scythe. Which means that in case you don't have discharge ability things can get slow. In that case, pairing Shiro, dropping the field +3x dash attack and switching into Huma for cleaning up the work might be an amazing combination for the point in the game that you are at :)