Does a swarm monger druid get an animal companion if they take Animal Ally?

Question

If a swarm monger druid takes the Nature Soul and Animal Ally feat, can the swarm monger have a rat familiar and a dire rat animal companion? Would the final sentence of Animal ally bring the dire rat to regular animal companion status instead of the -4?

Animal Ally

You gain an animal companion as if you were a druid of your character level –3 from the following list: badger, bird, camel, cat (small), dire rat, dog, horse, pony, snake (viper), or wolf. If you later gain an animal companion through another source (such as the Animal domain, divine bond, hunter’s bond, mount, or nature bond class features), the effective druid level granted by this feat stacks with that granted by other sources.

Answer 1

They would have one familiar and one animal companion.

The Swarm Monger druid archetype trades away its nature bond class feature, and gains a familiar. This means by default, they don't gain a druid domain or animal companion.

Their fecund familiar advances at their druid level (as per the archetype), but familiars are different from animal companions.

Let's take another look at the Animal Ally feat. First are the prerequisites:

Prerequisites: Nature Soul, character level 4th, must not have an animal companion or mount that advances as an animal companion.

The Swarm Monger druid can take the Nature Soul feat, and because they don't have an animal companion yet, they are eligible for the Animal Ally feat. Thus they gain an animal companion, but it's through the feat, and not through the druid class features.

The animal companion advances at the owner's character level -3.

The Animal Ally feat says that by default, the animal companion (from the feat) advances as though the owner was a druid of their character level -3. The last sentence says

If you later gain an animal companion through another source

But the Swarm Monger does not later gain an animal companion from their class, so their existing druid levels are irrelevant. Regardless of their prior druid levels, you treat them as a druid of 3 levels lower for the purpose of their animal companion advancement.