See for a biography of Isidore Keesing: Biografische Woordenboek van het Socialisme en de Arbeidersbeweging in Nederland.
In addition, a Jokos file (number 38048) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.The Jokos file reveals that a claim was lodged for compensation for valuables surrendered to the Lippmann-Rosenthal looting bank (L-claim, number 6284 / 1486).