I would recommend a Loop Node and pass it the shell array as the input. Inside the loop you’d add a Geofence Node to do the check. The Geofence Node takes a template, so you can combine the lat and lng values using the following template as the input to the Geofence Node:
{{ working.item.value.lat }}, {{ working.item.value.lng }}
The above template makes an assumption that you put each object in the array on the working.item payload path in the Loop Node configuration.