How do I get both Zero and Lexy unlock?
Yes you can, if you unlock Zero in night 3 work on paranormal research until it 400/1000 then in night 6 in day Time i think a magic shop will appear and you can buy a magic necklace for $1200 then in night 7 choose VIP room after that Lexy will appear then after night 7 is done she will be you’re second room mate and you can have a little scene with both her and zero.
Here is proof what i am saying 
265 days ago(+2)
Oh that Easy follow my step by step guide and you can get the scene with only Lexy.
Step 1: In night 2 when the power is out choose the “search for a vent or another way out to the room” (little note you can choose whatever to do in the vent it won’t matter).
Step 2: In night 3 after replacing the camera in the repair bay “tell zero to go back in her pod” then “restock soda wand” then “Clean up blood”
Step 3: In Night 4 do “Restock energy bars” then “vacuum booths”
After you done all three steps when you begin night 5 Lexy the shark will be unlocked.
The next night in the daytime lexy will make herself at home in jack black apartment and around there you will trigger the sex scene with lexy. (I think???)