Two beneficiaries live in UK: one is somewhat recalcitrant and requires the other UK resident to be an administrator.
other beneficiaries in Australia are not particularly against this but, would this be legal in NSW? They are all family.
Doesn't much matter what any one beneficiary might "require".
The main real-life argument against what you're asking about is
that it can be really inefficient to have an Administrator who is outside the jurisdiction.
It's also very hard to bring an effective action against a misbehaving remote Administrator.
Why can't a locally resident relative apply for Letters of Administration With The Will Attached?
It's easier than opposing an application by a would-be administrator who is outside the jurisdiction.