Temples

[Sinner]

The Healing line of temples is shared by the Brutii (Juno), Egyptians (Imhotep), Seleucids (Asklepios) and Britons (Brigantia), with the latter only able to build up to Large Temple (Sacred Circle), while the other three factions can build up to Pantheon.

The Trade line of temples is shared by the Brutii (Mercury), Carthaginians (Milqart), Greeks (Hermes), Numdians (Milqart) and Britons (Britannia), with the latter only able to build up to Large Temple (Sacred Circle), the Carthaginians and Numidians can build up to the Awesome Temple and the other two factions can build up to Pantheon.

The Violence line of temples is shared by the Brutii (Mars), Macedonians (Ares), Pontus (Hercules) and Germans (Donar), with the latter only able to build up to Large Temple (Sacred Circle), Pontus can build up to the Awesome Temple and the other two factions can build up to Pantheon.

The Fertility line of temples is shared by the Julii (Ceres), Egyptians (Isis) and Germans (Freyja), with the latter only able to build up to Large Temple (Sacred Circle), while the other two factions can build up to Pantheon.

The Fun line of temples is shared by the Julii (Bacchus), Armenians (Anahit), Egyptians (Osiris), Seleucids (Dionysus) and Thracians (Dionysus), with only the Armenians unable to build the Pantheon, being limited to the Awesome Temple.

The Leadership line of temples is shared by the Julii (Jupiter), Greeks (Athena) and Armenians (Armazd), with the latter only able to build up to Awesome Temple, while the other two factions can build up to Pantheon.

The Forge line of temples is shared by the Scipii (Vulcan), Selucids (Hephaestus) and Dacians (Zalmoxis), with the latter only able to build up to Large Temple (Sacred Circle), while the other two factions can build up to Pantheon.

The Law line of temples is shared by the Scipii (Saturn), Egyptians (Horus) and Scythians (Papay), with the latter only able to build up to Large Temple (Sacred Circle), while the other two factions can build up to Pantheon.

The Scipii's third temple line, Neptune (Naval), is unique to them.

The western Horse line of temples is something of an anomaly. The first three levels are only buildable by the Gauls (Epona) and the Spanish (Epona), but any Roman faction can build the last two levels, which in turn aren't buildable by the Gauls and Spanish. I always assumed that this was a typo/bug in the building file, but from what you've said it instead seems otherwise. Considering the limited window for the Romans to fully exploit this - they can only build up from the Sacred Circle - it's definitely worthwhile scouting Gallic and Spanish settlements before attacking them: if there's a Sacred Circle of Epona or any other temple then attack, but if there's only a Shrine or Sacred Grove of Epona, it's perhaps more worthwhile to hold off on any attack and wait until the Sacred Circle is built.

EDIT: Oops, also meant to add a link to my temple guide. As long as temples share the same type, ie. Trade, Fun, Law, etc, then one faction upgrade another faction's temples without problems. Note that the Macedonian temples to Ares are not the same as the Thracian temples to Ares - the former is a Violence temple, the latter is a Battle temple - and that the Carthaginians and Numidians share the same temples.