His own family must not have wanted him to sing or they could have moved this event to anywhere else in the world where this pastor has no say in what happens.
It looks like they wanted a specific “funeral mass” — a standard Catholic worship service — which also has standard implications, however.
He sang at the gravesite afterwards. Some here jeer, but at least if there was a chance that this could move the offender in a holier direction, it was taken. Maybe the grandmother would have approved of that.
Evangelical equivalents may exist. Some evangelical church members want the gospel to be preached at their funerals. (I would.) They’d probably want the people who would preach or sing alongside that to be known for serious Christian integrity, too. But if someone wanted to raise a tribute separately, most would not complain.