Are "shelter, shield" related?

I would imagine so. All the words have a common context of some kind of shelter.

As for North Shields and South Shields - "North and South Shields take their name from the word 'schele', meaning a temporary hut or shed. Shiels or shielings are usually found in the uplands where they were occupied by shepherds who could shield themselves from the wild weather." From here.

People forget that the modern Scottish border is relatively recent - the Kingdom of Northumbria was made up of the North-East of what is now England and the South-East of what is now Scotland.