When a safe-deposit box or other receptacle for the safekeeping of personal property is rented to two or more persons acting as co-executors, co-administrators, co-guardians, co-trustees or co-receivers, access to such safe-deposit box or other receptacle may be allowed as follows, as the contract of renting shall provide:
(a) by any one or more of such persons acting as co-executors;
(b) by any one or more of the persons acting as co-administrators, co-guardians, co-trustees or co-receivers, when authorized in a writing signed by the other person or all other persons so acting;
(c) by any agent authorized in a writing signed by all the persons acting as co-executors, co-administrators, co-guardians, co-trustees or co-receivers.