TurboTax does not allow you to create a separate state return if you file a joint federal return. The suggested solution is to create a “mock” separate return for Delaware for your husband.
How do I prepare a joint federal return and separate state returns?
Your husband should file a separate Delaware return. If you file jointly, Delaware will base your tax rate on your joint income. The tax will be the Delaware percentage of joint income.
Delaware says, "Generally, separate returns will be advantageous if both spouses have a Delaware adjusted gross income in excess of $9,400 or if only one spouse worked in Delaware."
See page 10 of Form 200-02 NR instructions