I'm not really sure, I honestly don't usually make my OCs plural except for Hadel, and I just kind of write him based on experiences- like he's a self insert so I base his plurality on mine. Plurality is a very vast and fluid thing, so there's many different ways to experience it, and trying to explain how one would write it to someone who (I'm assuming?) is non-plural would be a bit more tricky bc of that.

I suppose try and think of why they would have headmates and alters. For example all 3 of my alters have very clear purposes for me, and it's all in regards to my traumas and other mental diagnoses and symptoms. Waves of stress and psychosis and stuff. Lots of amnesia too if you're switching often bc of stressful events.

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-My persecutor and protector alter was formed because I had troubled standing up to my abusers. Now he is also just generally feisty or defensive (like a guard dog) with people, but it's obvious where all those emotions he has stemmed from. (As an example) you could reflect how an alter like this could even be troublesome because they are more aggressive (if even just verbally) while the host is shy and soft and easy to walk on. Picking up after his battles with people when they weren't necessary was always a stressful thing for me to come back to until we were able to talk it out and he settled down a bit more.

-My little / child alter was made to be a barrier against stress. They usually only front during times of severe stress or when I get extremely triggered. They can either block everything currently going on out and be sorta numb, happy go lucky, and playful, or if triggered while active can be overwhelming, extreme, intense. etc. Usually littles have both extremes. A sense of playful ageregessiveness vs a tantrum.

-My caretaker alter helps me- take care of myself lol. Calms me down when I have a panic attack, helps me keep track of things like meds and trying to stay away from negative influences or substances, etc etc. They can also front during times of stress in order to take the edge off for me, but since they don't get that numbing catatonia like my little does, it still stresses them out too. It's less of a distraction and moment of ignorant bliss and more of them taking the pain for me. My persecutor is like this too, but usually he's put in that spot only if I can't front myself and he's forced to.

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There's other things to consider ig like for my system, there is A LOT of co-fronting which can take form in several different ways but primarily it's two or more alters and/or headmates being able to talk and be present at the same time.
Cofronting can allow an alter or headmate to touch you physically (I often fall asleep being held or I can feel them touch my face, etc etc)
They can also "feel" or control certain parts of your body while you feel / control others, this is usually how members of a system will be sexually intimate with each other. A cofronting alter can also project onto objects, so maybe if your sense of their touch isn't so strong, they can project onto a pillow or a toy. etc etc.

There's also things like alters being an extension of self vs a whole unique individual.
Usually for my extensions, there's less cofronting and touching. Not entirely absent of it, but less. There's also overlap of traits a lot of the time, or when cofronting, it can be confusing to tell who I actively am.
While unique alters can be a lot more active with me, and it's a lot easier to tell who is explicitly fronting, however there can be more amnesia that comes with them fronting alone (there can still be a lot of it when it comes to extensions too, it's really based on stress).

I don't tend to have these, but other systems often gain characters from medias they enjoy as alters because it's a comfort thing- they distract systems from stress as well. They're no less valid than having an alter be unrelated to someone else's media, these would usually be less extension of selves and more unique separate individuals. Usually.

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Ig other tiny tidbits to keep in mind on how exactly to showcase it is, some systems are really open about the fact they are plural and who is currently fronting, while I find in person (and also with my system online as well), a lot of alters don't like to mark when they're currently fronting. They prefer it to be vague to others unless absolutely needing to- or feel comfortable specifying.
Usually there is an overall name an entire system can go by in person for general life things- usually the main host or most active's name, for example we use Ninya or Pest as a whole system while I, who'd usually be seen as the host (altho I don't personally like using the word host in this system for personal reasons) am named Jesse.

So what I mean by all that is, I in my day to day life don't really talk about being a system or talk about my alters in person aside from with my therapist. I barely do it online either. If my persecutor is fronting while we're at work, he'll go by my name. If someone online thinks it's me, he usually wont correct them. I don't tend to talk out loud to my system because I don't need to either, you'd truly tend to showcase who is fronting more out of how that alter acts in writing.

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But again, all systems are different. This is just a huge deep dive into my own mainly. I only ask with me opening up and sharing all of this with you guys, people don't try and investigate who is and isn't a part of my system. It's incredibly rude and while other systems are open about who is and isn't an alter in their life, we don't generally like to be.