It sort of depends on whether you have birdbaths in your sloped floor, or the overall slope is not correct.
Raising the drain to accommodate a second layer of tile may not be possible. I may be possble to remove the floor tile without compromising the liner...depends, it can be risky.
Many people put the floor tile in first, then cover it with the wall tile. This is not a requirement, it's just easier since the edge cuts look crappy if you don't get them straight - the wall tile going over them helps hide things. It is eminently possible to leave the wall tile in place and tile up to them. Industry standards call for that gap to be caulked rather than grouted. You could risk it and grout it, but it might fail. Doing it either way can look good...good workmanship is critical, though if you want it to look good.