As per present constitution of Nepal Nepalis residing abroad are allowed to have dual citizenship ( except for the people residing in SAARC countries).
Nepal government prepared an amendment the citizenship act of 2063 describing the process for getting dual citizenship but unfortunately parliament is dissolved. Hopefully next parliament will approve the Bill .

As per the bill Nepalis residing abroad can have dual citizenship with full rights except political and security concerned activities.
You need the proof that you were Nepalis citizen before and your parents were/are Nepali citizen.
so wait for 1-2 yrs