I think 30 mbps plan is more than suitable for 4 to 5 people whose main usage will be youtube ,
netflix etc. Since most of the sites are directly peered with jio and intelligent bandwidth management 5 people can enjoy stutter free videos. The problems comes when the use case is outside peered sphere,like downloads from some international servers or other work related stuffs, as less bandwidth can affect the user experience in a way when there is some international choking or something happens, say with 30 mbps speeds may gets less to 10mbps or some thing but with 100mbps plans u maybe getting 30 to 40 mbps during that times which is still good.
Just my thought