The point about a discretionary trust is that it creates a situation where the funds can be paid to a variety of objects thus destroying the power of any possible beneficiary to insist on any particular level of funds being paid to him.
Some trusts are called 'precatory'. They are particularly created to protect the fund against a wastrel beneficiary. They therefore have clauses or are in terms which make it extra difficult to put effective pressure on the trustees. Thus Atti is exactly right in saying that only full access to the terms can answer your question.
It is perhaps adding the difference between a power and a duty. Trustees have things they can do (powers) and things they must do (duties). If an act is a power, the trustees can only act if they are unanimous as to its exercise. If the act is a duty, they must fulfil it as soon as one says yes. Thus, here, there may be a power to make such a payment, but any one trustee can say no and block it.