It takes most chins who come from an ok home
at least a week to settle in to a new home, up to a month is not uncommon. Ones that have been neglected or abused can take months or even years to come around. New sights, sounds, smells, people, possibly other animals, etc, it's a lot to take in and process to figure out what is and isn't something to worry about. You need to earn their trust, they are smart critters (about as smart as a 2 year old human or a small parrot) and do remember past wrongs, they are quick to angry but slow to forgive, so you can't rush it. You need to give them a reason to and proof that they can trust you not to hurt them, they are weak prey animals with very little in the way of defense. They can runaway, slip fur, bite, and spray pee but that's about it and in a cage you've pretty much taken away the running away option.
The best thing to do is have patience, spend time with them, talk with them, read aloud, sing, just hang out in the room, pet them in the cage, and let them crawl around on you, stuff like that. Most chins also enjoy music and watching tv, some people will even leave a radio or tv on specifically for the chins if they are going to be gone all day. Go about your normal life, walk and talk normally, otherwise when you do go back to acting normal that will not be what they are use to and it can freak them out again. You don't need to sit in the dark, unless that is something you normally do, that might actually make you seem more creepy. Predators sit and wait in the dark, you want to prove you aren't a threat. Another thing that can help win them over is giving them things every time you enter the room, you don't want to give a treat more then once a day (once a week is better) but you can give chew sticks or bits of hay (pick a kind you don't normally fill their hay feeder with) as much as you want, you can also give them new toss or shredding toys. The idea is that you want them to associate you coming in the room with good things happening. So come in give treat, toy, or chew stick and continue on with what you are doing unless they act like they want to interact.
I would hold off on letting them have out of cage time until you have formed a bond, otherwise every time you grab them to put them back in the cage you are giving them a reason not to trust you. Also most chins don't like going back in their cage, like a little kid coming inside from playing. You can try making going back more exciting by putting a treat in the cage, new chews, or fresh hay, so they have a reason to want to go back.
Also chinchilla's personalities vary widely, some are more social, brave, and curious, others more shy, scared, and cautious and everything in between. Most chins don't like being picked up (but being held is ok, I guess once they realize you aren't going to eat them, lol) and are never actually cuddly unless something is wrong with them. There are exceptions, of the over a dozen chins I've had a couple were cuddly, but most prefer to hang out with you and climb on you not actually cuddle. Your best bet is to either let them come out of the cage into your arms, so they aren't being picked up. Or gently scoop them up, making sure to support them. Also make sure to get a hold on the base of the tail (as close to the body as you can otherwise you can break the tail) so they don't jump out of your hands if you move away from the cage or are standing up.
This might help with figuring out if they are male or female,
https://www.cuddlebugchinchillas.com/information/behavior/malesvfemales.html. There is also a lot of other useful info on that site too.