Hi,
the best way your nephew i feel can be involved in his investing process, learn alongside and make sound choices is refer to ET Wealth which comes every Monday. They have the top Equity funds listed - he can start small by using Paytm money or directly via individual MF sites/Cams and invest in 2-3 funds. Cams shares a monthly summary of investments which will give him a good idea of how his investments are doing.
Starting with safe, proven, large fund houses is the safest way forward.
My suggestion is to invest via coin(zerodha)/groww in these funds: