Princess Luna, even though she raises and lowers the moon, was an employee at Black Mesa.
Princess Cadence while she spreads her love and brightens everyone's day, also was an employee.
Her sister Princess Celestia's voice came through the intercom saying, "Princess Luna and Princess Cadence, you are required in the anomalous materials control room."
A guard pony who was waiting for them said, "Good morning, Princesses. It looks like you two are right on time today."
"Perhaps you were dazzled by our beautiful looks." Princess Luna's Royal Canterlot Voice echoed and the guard pony shook in his hooves a little bit.
"Oh yeah I was dazzled," the guard said. "Good looking and friendly. Everypony in the facilities are going to love you."
"Indeed," Princess Luna replied after lowering the volume of her voice.
After he stopped shaking, The guard pony smiled and said, "Please follow me."
Princess Luna said, "Forgive me if I withhold my enthusiasm."
The princesses head in, signed their names into the employee sign in sheet, went through the scanning process, and headed straight for the control room.
When they got there, their boss greeted them saying, "Good morning, Princesses, the Cutie Mark Crusaders are running late. Princess Luna, I need you to get the testing samples from the storage and bring it to the freight elevator, and Princess Cadence, I want you to head in to the test chamber and start the machine."
Princess Luna said, "We will do what you ask and we won't fail."
So, what was that? No, really. What the hell was that? So, randomly Luna and Cadence work at Black Mesa because plot reasons. And they are employees? Wouldn't they be like, I dunno, administrators? Is this the human world Black Mesa? Or is it an alternate universe pony version? Why do Cadence and Luna have any scientific merit to work in the anomalous research lab? Are they theoretical physicists? Last time I checked, Cadence and Luna didn't know jack about science. Just this first chapter baffles me, and then after I finish the chapter, I look down and see that there are 16 more. 16 more. 16 more. 16 MORE!? I'm not sure if I could even dream of plowing through them (though they are probably short) and I could wager they fail to provide any answers to this. Really, I bet this could be an excellent crossover (and it probably has been made one in the past multiple times) but this fic simply lacks the merit to be worth further reading to me.
If I could leave you with some parting advice, it would be to read over your writing. Try to read it as if you were a critic, that way you could catch yourself if the dialogue is janky, or you forget a comma, or if you simply think you need more words per chapter. Anyways, keep writing.
EDIT: Just read the description, apparently it IS an Equestrian version of Black Mesa.