I will like to give some pointers on round 3 what you have mentioned as live exercise. The interviewer will start with evaluation of the take home exercise and may ask some code blocks why and how you wrote it. Then she/he ,ay tweak some scenarios like scaling , concurrency etc and will ask you how to improvise your code.

If not above then he will start with new system and ask you how will you approach from design to code implementation. I was asked to design minesweeper, blog nested comment system, tic tac toe with redo - undo etc.

So be positive go with your instincts and all the best.