But is the Anbu soldier likely going to be a sensor-type or not, so how common are they?

One does not need to be a sensor-type just to be able to spot hidden presences, and beyond that, tracking is a skill essentially shared by all AnBu, sensor-type or not.

Like I said, even one Anbu agent would likely be able to wipe out the hideout in Falkreath.

They just really weak in general. We see they die to the most inconvenient characters. Idk who other guy is, but I just know Anbu weak.

Not really. Rather the Anbus are simply utilized as a benchmark to show how strong the characters capable of defeating them are

I'm really confused, can 1 Anbu survive 1000 citizens attacking.

Possibly, depends on the Anbu I'd say.

With prep dark brotherhood negs

What kind of prep do you have in mind?

I was thinking poison, disguises, weapons available to them that can interfere and adapt to Anbu's abilities and techniques, and since they are a group, they would have strategies and backup plans.

Was responding to them^^^,but that's logical