This general issue has probably been discussed ad nauseum, but I want
to make sure my specific idea isn't going to blow up the Earth.

I have a small PA amp driving a single 8 ohm speaker that I use for
security monitoring in my retail store (mic in store, speaker in
office). I want to expand the system by adding 2 more speakers in
other areas.

If I go out and buy 2 cheap 4 ohm speakers, can I connect all three ( 8
+ 4 + 4 ) in series to my amps 16 ohm terminals?

Quality is not a big concern here (as long as it's not ridiculous). I
just want to avoid damaging the amp (or as stated above, destroying the
planet).

BTW the amp as terminals for 4 ohm, 8 ohm, 16 ohm and 70V connections.
Is there a better solution than what I'm suggesting?

Thanks in advance for all wisdom and advice.
David