I would suggest moving the site several feet outside where they marked with the flags, PLUS, use EXTREME caution when digging along that side of the site, they have been known to miss the mark when locating stuff unground.
At least if you don't move those flags, and now that you have pics of it, if you do damage something it is on them, but if you do damage something buried it could be very dangerous, thus my warning to use extreme caution in that area.
Digging or not I would totally avoid setting up a pool over where they have marked, if your luck is anything like mine, as soon as you get the pool full there will be someone knocking on your door telling you they need to dig up something and you will have to drain the pool and move it out of their way!