Hope your parents do speak or understand Hindi if so should not be any problem because up to Doha there will Nepalese speaking Crew and onward Doha there will(100% sure) Hindi speaking Crew(Air Hostesses and Stewards) and in DC immigration also they can ask for hindi speaking immigration officer.Nowdays all major Airlines(even in AA,Delta,US and Northwest Airlines)international flights and major Airport's arrival Immigration counter have Hindi speaking crew and staff.HAAMILE DHOTI BHANER HELA GAREPANI DHOTIKO BHASA HINDI(URDU) 3rd MOST SPEAKING LANGUAGE (after english and chinese) IN THE WORLD BHAI SAKYO.