You can write.

You just need to pare it back for screenwriting (I'm guilty of this too), edit yourself, give us the crucial visuals that this spot is infamous for. Your audience needs to see it and feel it.

Case in point:
The road makes switchbacks as it moves up the side of the
mountains

You use the technical term of switchback minus all the scary descriptive words you could use such as: steep inclines, hairpin bends, wild curves, perilous drops, dizzying, treacherous, no guard rails etc.

He drives at the helm of his dream RV, at once
steering as he views the road, and at another time hitting
the brakes or jamming the accelerator.

So, you want to describe something like -

Neil, 60s, at the wheel of his prized RV,  expertly navigating the perilous hairpin bends of Dead Man Pass, or perhaps he's nervous, sweating, jamming on the brakes, wildly accelerating out of corners,, dropping gears etc. The card players in the back should by this time be squealing from being thrown around - at least the females.

A quick search of Dead Man Pass tells me, under a headline of ' the most dangerous and spectacular roads', this:

This infamous road is tightly hairpinned and bumped, an exquisite winding mountain drive with sharp and blind curves and hairpin (bends) switchbacks leading the traveler over the mountains. Road signs along this route caution tractor-trailer operators to go as slow as 18 mph and chain up during the winter to ensure a safe trip to the top.

That tells me it's a white-knuckle ride that even the most experienced driver might  balk at. Gimme that!

So, is this turning into a cautionary tale about ignorant white twats encroaching on sacred land?

But then we come to an abandoned mine... Was there a Keep Out sign? Was it cause Jeff threw a rock into the old hotel?
Bats, and Alexios?

I think you actually need a catalyst for Alexios unleashing the bats.
The story is just a bit unfocused for me as if you couldn't quite decide which story to tell.

On a tech side there's quite a bit of unnecessary and passive additions to action lines, like this:

The BATTERING INTENSIFIES, The RV shakes from it.
The group fights off the bats. They flail at the tormenting
intruders. (how?)
Anna has more trouble fending them off.  (Show us)
The four of them flail to brush off the attackers. (lazy, sorry) are your actors to improvise here?
He lets go a SHOTGUN BLAST through the front door.  He 'lets go' further on with that shotgun too. Try something straight to the point ike:

Neil raises the shotgun, blasts a hole through the door.

Are you a prose writer usually, newish to screenwriting?

Just as a P.S. I didn't read this one earlier cause the title didn't grab me.
The logline did appeal, even though it had a somewhat familiar feel.

I'd like to see you take another stab at this.

The previous reviewers have things well covered, and given you plenty to work on, so I won't pile on.

I did like the visuals of the bat swarm, though, I agree that the devastation inside the RV would be more swift and complete -- and, in no way could the four survive the onslaught as described.

I hated the four visitors. If you could have given me a reason for Alexio's actions instead of leaving me to guess, then perhaps I could have enjoyed their demise (and, yes, they should have died.)

There's a base to work from here, so good job on getting it to the page.

Good writing. I would, however, make the eco-sliming family nastier. You describe Neil as a CEO -- why not make him CEO of an oil or mining company. Profit is king to him, and anything that stands in the way of said profits -- like environmental regs -- are evil. And maybe Mona got to be the second wife because she slavishly agrees with everything he says and does. And maybe Anna and Jeff are spoiled brats who don't understand why they have to drive around in an RV instead of buzzing around in a helicopter.

I do question why the guy in the cave is named Alexios and wears a turban. This is an American desert -- why isn't this guy a native-American shaman? Finally, the bat attack was well written, but the payback didn't go far enough. The insurance company will compensate the family for the loss of the RV, so how much of a lesson do they really learn?