Indonesian mereka and beliau: etymologies?

This is really directed to Roger, who has been a big help with my
Singala/Bahasa Wijaya project, but someone else on the list might
know as well.

I'm struggling with Singala pronouns, deciding what to keep and
under what forms.  I've kept the Indonesian saya which Doug Cooper's
list derives from Sanskrit for "assistant, companion."  I've also
kept kita.  One problem I'm having, however, is what to do with
mereka and beliau.

Are they derived from Austronesian?  The reconstructed forms for 3rd
person are *ia and *siDa and the only thing I can find that looks
anything close to mereka is a stretch of the imagination (Malagasy's
nedala).  Is mereka derived from an Indic source like saya?

Beliau looks more Austronesian than mereka, but I can't break it
down.  While I'm at it, I might as well ask about the etymologies of
Malay "beta" and "patik" as pronouns relating to royalty.

Incidentally, while researching for Singala pronouns, I stumbled
across the Austronesian reconstructions and for Proto-Sud-Sulawesi I
found the source "Mills (1975)" - someone I know? ;)

Anyway, thanks for the assistance (and your patience)!

Cheers,
Eamon