User, Role and Environment

Hello Folks,

We are working on data splitting between two part, and also need to separate users with their roles and what are the security they have. below are the question i have..

1. Need to separate the users with assigned role. After separating the users will one set of user already have access of production environment and second set of user will access the another custom production environment so which table should i checked

2. How to modified the security between both set of users based company level.

Kindly advised and give your valuable suggestion on the same.

Thanks

Ram