Well, that depends on desc_strat.txt:

Ankyra has faction_creator scythia --> Arverni
and sub_faction gauls --> Aedui
So it will rebel to Aedui after being upgraded to the next town lvl. It does not rebel to the "nearest" barb faction, it will never rebel to Getai for example.

Kyrene has:
faction_creator romans_julii --> AS
sub_faction numidia --> Ptolemaioi
So it will rebel to AS and then to Ptolies after being upgraded.


If of course Kyrene or Ankyra would be conquered by let's say the Romans and they would build the next town lvl, it would rebel to Eleutheroi.