Model.php

<?php

class EducationDetail extends Model{

  fatherEducationLevel{
    return $this->belongsToOne('EducationLevel');
  }

  motherEducationLevel{
    return $this->belongsToOne('EducationLevel');
  }

  sisterEducationLevel{
    return $this->belongsToOne('EducationLevel');
  }
}

class EducationLevel extends Model{
  
  public $table = 'education_levels';
  
  // 
  public function educationDetails(){
    return $this->hasMany('EducationLevel');
  }
  
  // ????
  public function educationDetails(){
    return $this->hasMany('EducationLevel');
  }
  
  // ????
  public function educationDetails(){
    return $this->hasMany('EducationLevel');
  }
}

I think, just one func educationDetailsOfApplication below is enough

public function educationDetailsOfApplication(){
    return $this->hasMany('EducationDetails');
}