We are remodeling the kitchen and want to use marble or granite tile for the countertop with no grout lines. What should we use for the underlayment and what to use for the bullnose, please advise, thanks in advance

we bought a home and are slowly remodeling it. the major problem is the bathroom. the last owners did a horrible job with the tile in the shower. it is all different shapes and sizes. where they didnt have triangle pieces, they just filled it in with the cement stuff. :( its only a couple months old with a few cracks. is there an easy way to remove the whole tile job and start over? i know tile is supposed to be permanant. and with all the cement they used on the hardibacker board, it looks solid. do i just go at it with a hammer? is there an easier way to remove all of it? thank you