var PersonProto = {
    name: '',
    surname: '',
    birthday: '',
    id: 0,
};

var mkPerson = function (name, surname, birthday, id) {
    var sibling,
        res = Object.create(PersonProto);
    res.name = name;
    res.surname = surname;
    res.birthday = birthday;
    res.children = [];
    res.sibling = [];
    res.mother = null;
    res.father = null;
    res.id = id;
    return {
        setMother: function (mother) {
         res.mother = mother;
         res.sibling = mother.getChildren();
         mother.getChildren().push(res);
        },
        setFather: function (father) {
          res.father = father;
          father.getChildren().push(res);
        },
        getSibling: function () {
          if (res.mother !== null) {
             sibling = res.mother.getChildren();
             sibling.splice(sibling.indexOf(res), 1);
             return sibling;
          }
          else if (res.father !== null) {
             sibling = res.father.getChildren();
             sibling.splice(sibling.indexOf(res), 1);
             return sibling;
          }
          else {
             return [];
          }
        },
        getChildren: function () {
          return res.children;
        }
    }
};

var syn = mkPerson('Syn', 'fsasfafas', '1996-10-10', 15);
var mama = mkPerson('Mama', 'aaaa', '1966-10-10', 16);
var tata = mkPerson('Tata', 'bbbb', '1966-10-10', 16);
var corka = mkPerson('Corka', 'cccc', '1966-10-10', 16);
var dziadek = mkPerson('Dziadek', 'bbasfasfbb', '1966-10-10', 16);
var babcia = mkPerson('Babcia', 'bfasasfb', '1966-10-10', 16);
var syn2 = mkPerson('Syn2', 'fsasfafas', '1996-10-10', 15);

syn.setMother(mama);
syn.setFather(tata);
syn2.setMother(mama);
syn2.setFather(tata);
corka.setMother(mama);
corka.setFather(tata);
mama.setMother(babcia);
mama.setFather(dziadek);


console.log(corka.getSibling());