Where there is no sufficient evidence that two joint tenants or tenants by the entirety have died otherwise than simultaneously the property so held shall be distributed one-half as if one had survived and one-half as if the other had survived. If there are more than two joint tenants and all of them have so died the property thus distributed shall be in the proportion that one bears to the whole number of joint tenants. The term “joint tenants” includes owners of property held under circumstances which entitled one or more to the whole of the property on the death of the other or others.