Dear Dhruv, thanks for your question.
Firstly you can apply for Masters in relevant field if you have academic gap and you have been gaining work experience in that gap. But you will need to provide all required experience documents for the same. Universities would be happy to consider if you meet entry requirements.
Secondly, for your cousin who has already completed a masters here need to demonstrate how he utilised this degree but wasn't fruitful and how the chosen masters course would benefit him. If he studied M.Com, but has been working in marketing and sales field, and wants to grow further, he can do MBA marketing.
I hope this helps! Feel free to drop in more of your queries.