Did the tile setter bid on a complicated pattern? this is not something to spring on them when they walk in the door.

Instead of marking it on the floor, mark out the dimensions of the floor onto cardboard (old boxes), create the stream pattern on that with the whole and partial sheets, and have the tiler move the tile sheets to the bathroom to lay them.

Do it close to the bathroom, of course.

You can use bits of hot glue to hold stray pebbles into place on the sheets.

That sounds like a good idea. I did tell the estimator guy about the pattern and showed him the tile, so that shouldn't be a surprise to them.