State tax filing

No, the only states that have reciprocity with Pennsylvania are Indiana, Maryland, New Jersey, Ohio, Virginia, or West Virginia. (Which states have reciprocal agreements?)

It is expected that it will "appear" your income is double, since you report $25,000 to each state. ‌However, the credit for taxes paid to other states, will reduce your tax expense for Delaware. ‌In order to report this, make sure after you check the box to take the credit for taxes paid to other states, you also report the income and Pennsylvania tax paid on the next screen.