So DS seems to be training himself, not sure how to rectify it.

[purplemurple1]

He will only wee standing up and goes to a quite part of the garden. We are v.v. rural (not UK) and most guys (and some women) do similar.

So he obviously knows he needs to go in plenty of time but will not go to the potty and absolutly won't sit down for a wee. He has tried to wee in the toilet but of course is too short to do this when standing and won't use the step stool.

Can they even learn to wee standing when they are so little and not wet their clothes?
Should we just skip the potty altogether?

Yes, skip the potty.

You'll have to find some sort of bribery to get him on to a stool for a standing wee into a toilet.

Where does he poo?

Generally next to the changing table, but if we are outside he just goes where ever but we've two large dogs and are on constant garden poo clean up so he will have seen lots out in the garden.

I have started showing him it in the toilet when putting his there from his nappy in the hope he will start to get the hang of that being where it goes.

we haven't done lots of nappy free time yet and he only poos in the morning so normally has his nappy on still when pooing.

What happens if you put some (brightly coloured??) ping pong balls in the toilet as target practice? Might that encourage him to use the loo?

Tbh I'd just thourght he had to sit down so haven't encouraged him to use the loo standing at all. We are going to go with it and have moved a step stool he likes to the loo and sill see how he gets on today with at least standing on it there.
something in the loo to aim at could be a good idea for later though.