Can I take the exams of all three years (BBA) together?

Yes, you can take the exam of last year. If you failed in previous year's exam then you will be allowed to give all semester exams together. So, clear all the exams, study well and take your degree with a good score.

It's not possible. You need to study for 3 years as the guidelines of UGC to be certified as a graduate.

No, you cannot. There are rules and regulations which every student and college or university has to follow. This is a 3-year course which you will complete at least in three years.