When you hire a family member, i.e. a nephew, do you by law have to provide workmans comp ins on them

If you mean hiring for your business, yes they have to have all benefits any other employee has. Why would it be otherwise, they would still be an employee?

Tick

Tickle is correct on this one 100%. Of course you must provide worker's comp as they are an employee. Makes no difference what kind of relative they are to you, they are still an employee and if they are injured on the job they need that insurance paid for them.