There are two different options to get married in India. Special Marriage Act and hindu marriage. If you are hindu, which I believe you are , the process is simple and will take only couple of days. For Special marriage act it takes about a month. Please google and find the difference.
As for resource, you need to hire a lawyer. Go to Tees Hazari court in Delhi and you can see 100s of lawyer willing to help you with the process. You will have an option to negotiate the price if you go that route. You can even look up online and book on advance but be prepared to pay premium charges. The lawyer will technically wed you guys at Arya Samaj mandir and then later register the marriage at registrar of marriage. You can do these on your own but in India money talks so having lawyer will smoothen the process. Be prepared to take lot of pictures and if possible invite your parents to come to India. It will look good at the interview. Also make sure the Arya temple isn’t a fake one. It should look like a real temple and not some shop.
Again this is only if you are hindu. You can also get certificate from ministry of foreign affairs in Kathmandu that states that you both are unmarried in Nepal. It May or mayn’t be required but good to have. Please go through their requirement for it. I think its called marital status certificate or some similar.
https://nepalconsular.gov.np/np/service/4
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