Joe Watts did indeed grow up on Staten Island. His father was a truck driver on the Staten Island piers. His dad is from Manhattan. His mom is all Italian and grew up in Manhattan and the bronx.
Not sure about his siblings and " the German" moniker .

Watts is actually Welsh on his father's side

Yes, so why " the German" ?
his mom was Sicilian which I found interesting but yet not shocked considering he hung with all Italians. I imagine he grew up with Italian culture.