Singapore contract

Mr X, a timber merchant with business interests in Singapore and Malaysia, entered into a written agreement with his grandson, Y. Under the terms of this agreement, which was in effect the sale of X\'s businesses to Y, it provided that upon the death of X, Y would pay X\'s widow, Mdm Z, an annuity of SGD 2,000 per month

How to get him to pay since he refuses? Without large court costs.