Interceptor is not related to first two games.
I'm not a lore geek but imho, none are, in fact; even first two are alternate realities not sequencial events.
So, there no overarching time line in the series to be had, each game is rather a separate alternative reality.
This is utter bollocks. Every game after the first makes it abundantly clear that TFTD followed directly on from the original UFO. Apocalypse is explicitly set after these first two alien wars - the very existence of the city you're defending comes about because of the events of those games.
If you read the starting ufopaedia in Interceptor, it describes both the first two alien wars (UFO and Terror From the Deep), and mentions that the city from Apocalypse (mega-primus) is under construction. The obvious conclusion is that Interceptor comes third chronologically, and is followed by Apocalypse.
Now, you can disregard Interceptor if you don't like it, or feel it doesn't fit with the other games, or its plot doesn't make sense. That's totally fine, we all have our preferences about what does and doesn't work for a series, but there's a clear order of events written into the games, no need for any magical alternative realities or whatever.
Enforcer, on the other hand... nobody cares.