It depends on the terms of the scheme. The usual thing is that the trustees have the power to decide who receives the benefits if the original beneficiary dies, they look at who has been nominated but they are not bound by it.
This may seem strange, that the trustees have the power to decide how a persons pension assets are distributed, but the reasoning is that circumstances may have changed between the pension being set up and the beneficiary dying, it may be a span of decades. The beneficiary may not have updated their wishes.
I do not know if there is a way to indicate to trustees the beneficiaries wishes other than the nomination process.