What is maximum limits allowed for members in Google Group?
Do you mean in Google+, in GMail, or in Google Groups proper (I don't think there' s a limit to the latter)?
Please note that q mentions 'Google Groups' Properly:)
In Google Groups proper, you associate yourself with Google Groups (something akin to forums). There's no limit to the number of people who can belong to a particular group. There may be a limit to the number of groups you can belong too, but I have experimented with it in the past and "subscribed" to far more groups than I could scan, let alone read!