2nd wife means no legal entitlement already.

unless there is a written will specifically named him as part of the beneficiary.

There is the problem of a property with joint name.

Since the other 2/3 owner refuse to apportion the rental income, the only solution is through legal process to claim back.
But the cost of legal process may outweight the 1/3 rental income.

A better solution is to propose the other 2/3 owner to buy over the 1/3 share.

As the property technically cannot be sold or rent (sign new tenant agreement), without all party agree.
So propose to the other 2/3 portion owner, stated there may be future problematic/deadlock situation, if not buying over the 1/3 share, as if 1/3 share owner doesn't want to sign, nothing can be done on the property, which virtually all party get nothing from the property.