public IEnumerable <Person> GetBrothersInLaw()
        {
            var bil = new List <Person>();

            var spouseMaleSiblings =
                Spouse?.First().Relationships.GetSiblings()
                ?.Where(x => x.Gender == Gender.Male);

            if (spouseMaleSiblings?.Any() == true)
            {
                bil.AddRange(spouseMaleSiblings);
            }

            var femaleSiblings = Siblings?.Where(x => x.Gender == Gender.Female) ?? Enumerable.Empty <Person>();

            foreach (var motherFemaleChild in femaleSiblings)
            {
                var spouse = motherFemaleChild.Relationships.GetSpouse();

                if (spouse?.Any() == true)
                {
                    bil.Add(spouse.First());
                }
            }

            return(bil);
        }