Are you sure they are breaking social distancing rules? They could be providing key services to others in the community that could be misunderstood as a breach.
Try and have a chat with them – obviously while keeping the correct social distance – and remind them of the rules.
If you don’t feel comfortable speaking to them directly, you could always ask another neighbour to chat to them instead or drop a friendly note through their door
If you have a neighbours’ WhatsApp group, you could send a friendly reminder via this channel as well
Put up our social distancing poster – PDF 1MB to remind people about social distancing, or again maybe just drop it through your neighbour’s door.