IIT

In my opinion resonance is best for IIT preparation for freshers as well as repeaters. Best of luck.

Kotak is the best in term of IIT preparation. If you spending money then Kotak is the best option as it has a better atmosphere for study and competition.

For JEE Mains preparation, I suggest you Resonance.

Prepare on your own. Don't rely on any coaching institute, instead get a good internet connection and start studying online. This will be the best way to study and get the most out of your time. What you need is to focus your class 12th books Basics. NCERT textbooks are the best for IIT preparation. Just go through the books very thoroughly and then finally give lots of mock tests etc. To get a nice practice.

Click on the link for more details:-https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-india-accepting-jee-mains/44-2-0-0-6244

JEE Mains and you have to secure above 200 marks to get good NITs or IIITs. You have to take PCM in 12th and must clear the same with at least 75% to appear for IIT JEE. If you score less than 75% then you cant appear for JEE Mains. So, also reappear for 12th to appear for JEE Mains.

You say him to join the counseling process by JoSAA as rank is good, then she will sure get Good IITs. Please check the college closing rank for different IITs:
http://josaa.nic.in/Result2016/result/OpeningClosingRank.aspx

To get admission through JAC, you just have to score the minimum percentage required in these colleges, I. e, 70%. Moreover, you need to focus more on the Mains paper.

If you want to know in which colleges you get seat please go through the link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
And fill all the options and choose the best college which suits for you. All the best.

You are eligible for appearing in JEE Mains if you have done 12th board from any Public School/ Board / University examination in Nepal recognised as equivalent to the 12th system by the Association of Indian Universities (AIU). You may, kindly, refer to following for further details:
http://jeemain.nic.in/webinfo/Public/Home.aspx