Best method for removal?

What do you think is the best way to remove these stains. Looks like rust but oxiclear hasn't touched it at all. There's quite a few around the property 

OxI clear isn’t for rust staining , this stuff works well but isn’t cheap , you can buy it in smaller quantities 

oxiclear is for girls @Clarkus84 ?, I've removed many of those stains over the years and, y'now  its quite profitable.

I've always used this https://www.bonnymans.co.uk/products/product.php?categoryID=1414&productID=6324

for those stains I would gently wire brush the stain dry to remove the excess rust- just makes it easier so you are down to the bare bones so to speak.

wet the area thoroughly with tap water and then make a paste, (some of the posher softwash guys call it a poultice to sound good and it makes them sound so professional), this is done with warm ro/"pure" water-boil it all in a kettle and pop it in a flask if you don't have hot, make a cream with oxalic acid and apply with a paint brush and leave for a few mins wire brush again to agitate and re-apply as and when needed, you say theres a fair few stains on the property so you can easily be monitoring progress as you move from one stain to another, have a small spray bottle with tap water in to wash away some of the oxalic acid cream/poultice  and re-apply as and when needed, you may also need to agitate the stain with a wire brush to get it working better, this way you are working on many stains but you can monitor progress as you go along.

once the stain has gone wash away all residue and maybe apply some hypo but only if it needs it, oxalic acid is present in most foods but is still a harmfull  product so please, wear ppe, good luck and this stuff will work if you put the time in to the job and remember that you are removing a layer one at a time  so patience is needed

sorry, I should add that you can use a nail brush for agitating the acid on the smaller areas so the wires from the brush won't mark the stone-my bad