N.Y. Est. Powers & Trusts Law § 10-6.7

§ 10-6.7 Exercise by all donees; exceptions\n Whenever a power of appointment, other than a power in a trustee to\ninvade trust principal under section 10-6.6 of this article or under the\nterms of the dispositive instrument, is created in two or more donees,\nall must unite in its exercise, unless the instrument creating such\npower provides otherwise. But, if before its execution, one or more of\nsuch donees dies or becomes incompetent, such power may be exercised by\nthe survivor or the competent donee, unless such exercise is explicitly\nbarred by the terms of the instrument creating such power.\n