Just use each

controllers.application\.js

import Controller from '@ember/controller';
import { inject as service } from '@ember/service';
import { action } from '@ember/object';

import { dependentKeyCompat } from '@ember/object/compat';

export default class ApplicationController extends Controller {
  @service store;
  
  appName = 'Ember Twiddle';

	constructor(){
    super(...arguments)
    
    const bRecord = this.store.createRecord('b', { title: 'bRecord', rowOrderPosition: 1 })
    const bRecord2 = this.store.createRecord('b', { title: 'bRecord2', rowOrderPosition: 0 })
    const bRecord3 = this.store.createRecord('b', { title: 'bRecord3', rowOrderPosition: 2 })
    
    this.aRecord = this.store.createRecord('a', {
      bRelation: [bRecord, bRecord2, bRecord3]
    });
    
  }

	@dependentKeyCompat
  get bRecords() {
    const rows = this.aRecord.bRelation.toArray()
    rows.sort((a, b) => {
      return a.rowOrderPosition > b.rowOrderPosition ? 1 : -1;
    });
    return rows;
  }

	@action
	bRecordDelete(bRecord) {
    bRecord.deleteRecord()
  }

	@action
	updatePosition(record, move) {
    const records = this.bRecords;
    let start = records.indexOf(record);
    
    if (move === -1) {
      let prev = records[start - 1];
      record.rowOrderPosition -= 1;
      prev.rowOrderPosition += 1;
    } else {
      let next = records[start + 1];
      record.rowOrderPosition += 1;
      next.rowOrderPosition -= 1;
    }
  }
}

helpers.eq\.js

import { helper } from '@ember/component/helper';

export default helper(function eq(params/*, hash*/) {
  return params[0] === params[1];
});

helpers.sum\.js

import { helper } from '@ember/component/helper';

export default helper(function sum(params/*, hash*/) {
  return params[0] + params[1];
});

models.a\.js

import Model from 'ember-data/model';
import { belongsTo, hasMany } from 'ember-data/relationships';
/*
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';
*/

export default class extends Model {
  changeTracker = {only: ['bRelation'], auto: true};
  @hasMany('b') bRelation;
}

models.b\.js

import Model, { attr } from '@ember-data/model';
import { recordIdentifierFor } from "@ember-data/store";

export default class extends Model {
	@attr('string') text;
	@attr('string') rowOrderPosition;
  
  get lid() {
    return recordIdentifierFor(this).lid;
  }
}

routes.application\.js

import Route from '@ember/routing/route';

export default Route.extend({
});

templates.application\.hbs

<ul>
        {{#each this.bRecords as |bRecord|}}
          <li data-stage-record-identifier={{bRecord.lid}}>
            <div>
              <pre>title: {{bRecord.title}}</pre>
            </div>
            <div>
              <pre>identifier: {{bRecord.lid}}</pre>
            </div>
            <div>
              <pre>rowOrderPosition: {{bRecord.rowOrderPosition}}</pre>
            </div>
            <button {{on "click" (fn this.bRecordDelete bRecord)}}>delete</button>
            {{#unless (eq bRecord.rowOrderPosition (sum this.bRecords.length -1))}}
            <button {{on "click" (fn this.updatePosition bRecord 1)}}>down</button>
            {{/unless}}
            {{#unless (eq bRecord.rowOrderPosition 0)}}
            <button {{on "click" (fn this.updatePosition bRecord -1)}}>up</button>
            {{/unless}}
          </li>
         {{/each}}
</ul>  
      <style>
      li {
      	font-size: 12px;
      	padding: 10px;
        outline: 1px solid red;
      }
      
      button {
        margin-top: 10px;
        padding: 3px;
      }
      </style>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-data": "3.18.0"
  }
}