Best Approach:

Have them get married as usual in the same way like जन्ती, श्वयेम्बर , invitation, party and so on. Take as many pictures as possible including videos. Make it look real. And also make court documents if needed. There won't be any doubt in this way. This is (like) a real wedding. Just have clear understanding with your friend that they don't do anything you don't like such as "this and that".

Once they are here, have them get divorced. And you marry her. Done. It is fair, clear and legal.