Difference between "Tu draw" and "Tu hwnt" and how to say "unauthorised"

I would like to buy a ready made Welsh language sign saying “No unauthorised persons beyond this point” but, as a result of experience, am wary of one without checking the Welsh first.

The commercial signs I have seen generally say something like:

“Dim personau heb awdurdod y tu draw i’r fan hon”

Checking this with the Helo Blod translation service gives instead:

“Dim mynediad heb ganiatâd y tu hwnt i’r fan hon”.

Unfortunately I can’t find a ready made sign with the Helo Blod version.

So, two lines of questioning.

First, what is the difference between “tu draw” and “tu hwnt”? According to my dictionary they both mean “beyond”, but which is right in the context of this sign? Is it a regional variation - I am in North Wales?

Secondly, in the context of the sign which is the most appropriate way to say “unauthorised”? The Welsh Academy dictionary seems to support the Helo Blod version (even though it isn’t a direct translation of the English), but is “Dim personau heb awdurdod …” acceptable Welsh usage? Would “Dim personau diawdurdod …” be better? Or is the whole “Dim personau …” construction best avoided?

Any help is most welcome - I have tried to work this out myself but have got rather stuck.

tu hwnt and tu draw are both fine (no regional difference as far as I know), and there’s no real difference.

The construction I would personally use would be the Helo Blod one - lit. “no entry without permission beyond this point”. The other example you give is lit. “No persons without authority beyond this point” and whilst they’re both saying more or less the same thing, personau is not a widely used word among native speakers as the plural of person, and could be confused with vicars/parsons/clergymen (which could make an interesting interpretation of the sign!)

Many thanks for the prompt response - most helpful. You have triggered a memory that for the plural of persons “pobl” would more normally be used, so possibly “Dim pobl heb awdurdod …” would be OK?