ayomide.
the BA interview is like all interviews, it's a process of ticking boxes, you need to give the answers that they are looking for.
The group discussion is watching how you interact with others
The one to one is all about you telling them that you have the relevant experience, so have some examples of situations ready (as it's always hard to think of them in an interview situation.)
The usual ones are, when you've gone that extra mile, when you've given excellent customer service, when you've recovered a bad situation, when you've worked as a team, when you've dealt with a personality clash, when you've had to work when you were demotivated, cultural awareness, etc etc
Hope this helps, let me know how you get on
When and where's the interview?