LB I am sorry for your loss, hadn't realised when I posted earlier that it was so recent. I did a quick search and found that people in Wales can go out to access public services and also to meet legal obligations which registering a death is so I think he's ok to go.
"When can I leave home?
You should only be outside of your home for very limited reasons, which include:
the need to obtain supplies and services for you or your household, for example food, medicine, and essential household maintenance. We encourage everyone to make this as infrequently as possible
to exercise, alone with members of your household or support bubble or with one person from another household. We encourage this to be done locally.
to access childcare and education
to access medical services
to access public services
to provide or access emergency assistance
to deposit and withdraw money from a bank or similar establishment
to provide care for or to help a vulnerable person; this includes getting food or medicines for them
to help the NHS by donating blood
for work purposes, or voluntary or charitable purposes, but only where it is not reasonably practicable to do this from home
to visit a cemetery, burial ground or garden of remembrance to pay your respects
to attend a place of worship
to attend a wedding, civil partnership or funeral if you are invited
to attend court or meet other legal obligations, or to vote
to escape a risk of illness or injury, such as for victims or people at risk of domestic abuse
to access services provided to victims of crime or domestic abuse or those at imminent risk of becoming victims
https://gov.wales/alert-level-4-frequently-asked-questions#section-58318