Flight
New York has many airports, but JFK or EWR would provide the best flights for international guests. EWR has the easiest access with a 2.5 hour drive and avoiding New York City. JFK is a 3 hour drive as it passes by the city.
Flight
Both airports - PHL & BWI - are roughly 1.5 hours from the wedding location. These would provide good flight options for domestic travelers.
Flight
Harrisburg airport is definitely the closest to the wedding location, about 45 minutes. However, it is a regional airport so flights are fewer and more expensive.