I wonder if one of the solutions wouldn't be also using something like :
<ng-container formGroupName="childGroup">
<input type="text" formControlName="childControl1">
</ng-container>
<input type="text" [formControl]="parentControl1">
<ng-container formGroupName="childGroup">
<input type="text" formControlName="childControl2">
</ng-container>
That way we would get ordering split. Though I am looking for answare if that is allowed to have separate 2 fromGroupName in same template. I am experimenting right now. What do you think guys?