>>938254373
>I should use "concat" in between prompts for different characters?
not quite. you would have multiple nodes for positive prompts and instead of leading the output a single positive prompt to the KSampler as you normally do, instead you lead each output of the positive prompts to a conditioning concat node.

inside each positive prompt are the separated prompts, like one node for scene description, another for 1girl description, another for 1boy description, then at the end you join them together with concat nodes (multiple nodes if you have more than 2 positive prompts). and at the end it goes into the KSampler.

also i'm just attaching images to identify myself, pay no attention