What are the consequences of section 3990402 25ba if crime is proven

My relative was arrested on 12jan 2022 in gurgaon and is in judicial custody now . We dont know what exactly happen because he is in custody and we couldn't meet him and ask him. But what we saw in chargesheet filled by police is that he is arrested under the section 399, 402 and 25-b- a . In chargesheet it is written that my relative is one of the 5 man having a wooden rod ( dnda) in hand sitting in a white car and doing planning about tge robbery . My relative has no previous criminal record and he is currently a student also . So i just want to know that how serious this matter is and what are the minimum and maximum consequences of this case can be if the proven guilty. Beacuse some lawyers are saying that he can even get life impriosonment. So i dont understand that only including in just a planning can get this harsh punishment. Please explain me this.