MRZ format confusion - trying to fill in forms, but my name order is different

My precise question: Is the MRZ format documented somewhere, such that I should purposefully fill in forms counter-intuitively so as to conform to the standard?

I have a Brunei passport (yes, what the hell is that?) and the format of my passport's MRZ is

PNBRN{FIRSTNAME}<{FAMILYNAME}<{OTHERNAMES}<<<<...

and indeed, the "Name" field (I only have one single name field) of my passport says

{FIRSTNAME} {FAMILYNAME} {OTHERNAMES}

I am worried that when filling in forms, that tell me to fill it in "exactly as in passport" and then go on to talk about first name and last name.

I notice that every other passport in the world puts the family name before the forename.

Shall I fill it in according to what I call myself or what the passport says?

Basically, I just hope that things don't go wrong because my names are in an unexpected order.