AMS-LHR with your experience (or anyone with customer contact experience) you have just as much chance of getting the job as someone flying for 20 years. BA does value previous airline experience but above all they are more intent on getting the 'right' people as everyone has to do a training course anyway.
The group interview is just all about how you interact with others. They are looking for all the usual things but be concious of your body language also. Eye contact, face people when you talk to them, acknowledge everyone in the group. And of course the obvious: follow the instructions the selectors give you, don't speak over anyone etc.
The 2-on-1 interview is highly scenario based with questions similar to (or some the same as) the ones in the online application form although if the question is one the same as the application form they will ask for a different example from you than the one you provided online.
Obviously they are looking for someone customer orientated. Also be sure to mention teamwork. They ask a lot about 'negative' experiences also. for example 'tell us about a time when you messed something up for a customer' or 'tell us about a time you didnt get along with a work colleague'. Don't be afraid to tell them about mistakes you have made (obviously don't tell them any BIG ones). These questions are centred around a resolution. You messed up, but how you resolved it in the end and turned it around to satisfy the customer.
Good luck!