how much is 1.85 lakh?
A little more than 10,000 PLN. Twice as much pay sounds great, until you realize that the cost of living for an Indian expat with wife and school age kid in Poland are going to be a lot more than twice the cost of living for an Indian native living in India. It's also going to be a good bit more than for a native Pole with a wife and school are kid living in Poland.
Things to take into account:
Expenses related to travel and relocation. Not only tickets, but visas, days of from work to travel to embassies, etc, all add up. If he stays in India, this expense is, of course, zero. Depends on whether he gets a relocation bonus or not, and how generous it is.
Loss of home court advantage. A Pole can live a lot cheaper in Poland than an foreigner, who doesn't speak the language, know how the "system" works, or have a network of family and friends.
Tuition for the child. That's going to cost a whole heap. ISK costs 60,000 PLN a year. That's 5000 PLN a month, each and every month of the year. He might opt for something cheaper, but that would probably represent a huge drop in quality compared to what he is currently getting in India. That drop in value has to be figured in as a cost.
Travel back home. Going to visit the folks and the in-laws will cost a LOT more than it would had he stayed in India. A funeral or wedding or two can wipe out any savings.
Keeping the wife occupied. In India, she has friends of her own ethnic/language/social group who she can socialize with. It's going to be hard if not impossible for her to find anyone in Poland. He will have to keep her occupied somehow from going stir crazy, and that's going to cost something.
Job networking. It's tempting to think that, being in Poland, an Indian would find it easier to break into the job market of the richer Western countries. It's probably harder, though, because back home, he has, or should have, an extensive network of colleagues who have worked in the West or even are working there right now. Poland doesn't make as much sense as a "stepping stone".