Eloquent Model for a family tree.One can find parents, children and partner through relations.

Member.php

<?php

namespace SaveMyData\Models;

use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent;
use Illuminate\Support\Carbon;
use Illuminate\Support\Collection;

class Member extends Model
{
    use SoftDeletes;

    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'first_name',
        'last_name',
        'nick_name',
        'birthday',
        'sex_id',
        'user_id',
        'obit',
        'mother_id',
        'father_id',
    ];

    private $parent;
    private $kids;

    /**
     * Getting parents if available
     *
     * Member constructor.
     */
    public function __construct()
    {
        if (! is_null($this->mother_id)) {

            $this->mother->with('mother');
        }
        if (! is_null($this->father_id)) {
            $this->father->with('father');
        }
    }

    /**
     * @return Eloquent\Relations\BelongsToMany
     */
    public function family()
    {
        return $this->belongsToMany('\SaveMyData\Models\Family', 'family_member', 'member_id', 'family_id')
            ->withPivot('is_member_by_heredity');
    }

    /**
     * @return Eloquent\Relations\BelongsTo
     */
    public function user()
    {
        return $this->belongsTo('\SaveMyData\Models\User');
    }

    /**
     * @return Eloquent\Relations\BelongsTo
     */
    public function sex()
    {
        return $this->belongsTo('\SaveMyData\Models\Sex');
    }

    /**
     * @return Eloquent\Relations\BelongsTo
     */
    public function mother()
    {
        $mother = $this->belongsTo('\SaveMyData\Models\Member', 'mother_id');

        if (isset($mother->kids)) {
            $mother->kids->merge($mother);
        }
        return $mother;
    }

    /**
     * @return Eloquent\Relations\BelongsTo
     */
    public function father()
    {
        $father = $this->belongsTo('\SaveMyData\Models\Member', 'father_id');

        if (isset($father->kids)) {
            $father->kids->merge($father);
        }
        return $father;
    }

    /**
     * Returns all children of member. Determines if $this member is female or male
     *
     * @return Eloquent\Relations\HasMany
     */
    public function children()
    {
        $foreignKey = 'mother_id';

        if ($this->sex_id == 1) {
            $foreignKey = 'father_id';
        }

        $children = $this->hasMany('\SaveMyData\Models\Member', $foreignKey);

        foreach ($children as $child) {
            $child->parent = $this;
        }
        return $children;
    }

    /**
     * @return Eloquent\Relations\BelongsToMany
     */
    public function relation()
    {
        return $this->belongsToMany('\SaveMyData\Models\Relation', 'relation_member', 'member_id', 'relation_id');
    }

    /**
     * Returns a collection of members (which are partners due to relations)
     *
     * @return Collection
     */
    public function partner()
    {
        $relations = $this->relation()->get();
        $partners = new Collection();

        foreach ($relations as $relation) {
            foreach ($relation->member as $partner) {
                if ($partner->id != $this->id) {

                    $partners->push($partner);
                }
            }
        }

        return $partners;
    }

    /**
     * Returns nick_name if is filled. Otherwise first_name
     *
     * @return mixed
     */
    public function name()
    {
        $first_name = $this->first_name;
        $nick_name = $this->nick_name;

        if (!is_null($nick_name)) {

            return $nick_name;
        } else {

            return $first_name;
        }
    }

    /**
     * Returns age of member
     *
     * @return int
     */
    public function age()
    {
        $age = Carbon::parse($this->birthday)->age;

        return $age;
    }
}