Is there any way I can just skim over the existing tiles then fix the
new tiles on this surface ?

You can (but miss out the "skimming" step), but before you give up on
removing the tiles, have you tried removing them with a flat chisel bit in
an SDS drill set to hammer only?

When removing tiles, I've always found it very difficult and damaging to
remove with cold chisel and hammer, whilst the SDS chisel sees them flinging
themselves off the wall whole, with minimal damage to the surface. I think
the high frequency hammering is the key.

Christian.