How are PCBs with castellated pins arranged in a panel?
You put full pads with drill holes centered on the outline of the PCB with the soldermask pulled back as usual. Follow your PCB manufacturer's recommendations on hole and pad sizes and spacing.
The castellated edge has to be routed, but there is nothing stopping you from V-grooving other edges or using mouse bites to panelize.
Plating portions of the edges is a different process from simply chopping through the plated holes, and may require some additional information to be passed to the supplier. Even if you don't want to panelize the boards, the PCB maker has to panelize them and will need to place supports.