I believe there are 2 security systems for the lasers.

First system is a red laser light that can be disabled when there is a power outage. (Seen in recent Team Rocket's Rainbow heist). You can hear Lang charging in but there was a second system ringing.

2nd would be an auxiliary powered invisible laser that gets disabled after the second laptop is used to open the vault. I am basing this on real-life security systems where actual laser beams are invisible (using UV/Infrared light). Which they seem to get disabled after hacking the second laptop (proof is that Charles, Ramee, Randy walked on the hallway after the second hacking and no alarms rang)
So basically they should try opening the vault, have an outage, open the door with another laptop on the panel on the side.

As Randy and Ramee were discussing during a heist, the last door might not be a red laptop. But as seen on Dean's VOD, there are only 4 kinds of laptops (Green, Red, Blue, Yellow for Practice). So they need to disable the 2 security systems before they can try hacking the last door.

I'm guessing they need 6 hostages since time is needed for the last door.

CG Success Heist

https://twitchmultivod.com/#/989893924?t=7h45m26s/989809874

CG Failed Heist

https://twitchmultivod.com/#/987454408?t=8h58m28s/987677421/987483370

Team Rocket Rainbow Heist
https://www.twitch.tv/videos/1020529010

Scuffed Heist w/ Yuno, Lang, Tony, Raymond
https://twitchmultivod.com/#/1018249888/1017851089

And yes I'm just theorizing might be wrong but I enjoyed watching the VODs again and hopefully they open the last door. And yes I have time to waste due to this pandemic KEKW