Very rough estimate using Google Earth as a source:
Chetumal (somewhat protected by a peninsula) - 136,000
Bacalar (just north of Chetumal, west end of a lake barely inland) - 10,000
Felipe Carrillo Puerto (a bit north of Bacalar, and a bit further inland) - 65,000
I pray the Mexicans got them inland. As Sender noted, there is some height in Chetumal.
Finally got here, long day.
sw
Oops, I forgot you had already listed the towns and populations. Sorry I repeated.