Travertine pool pavers cleaning

I’m after some advice about how to go about cleaning 600x400mmx30 thick filled premium pavers. My large pool paving project has gone rather slow over the months my pavers stuck down on concrete surround slab have become stained from the weather elements I haven’t grouted them as yet just been tryna cover as I go with tarpaulins to keep the rain out. Is it best to grout the sections as I go and arrange to have the pavers cleaned professionally before sealing? If I cudv done it again I wudv paid a contractor to do within a week but iv been doing the job on my own and the rain is unpredictable
The best course of action for my situation wud be much appreciated from any trade professionals