Don't Know What To Do!!!

No. If Randall is a boy, you can't. Even if you could, you would need a tank for QT (which should be a minimum of 1 month).
You can't keep boys together, and shouldn't keep boys and girls together because you risk breeding as well as the female being bullied by the male to breed.

I'm sorry.

I wouldnt really ever advised purchasing any animals that is sick because you feel bad about them. It never usually ends well and you may put in alot of effort and end up being hurt What I'd advise you to do is report them to an animal welfare organisation and hopefully something can be done for the little critter xx but from the sounds of things, it is too far gone if it has a pencil thin tail

Randall had a pencil thin tail and i brought him back to perfect health... But i'll report it to an animal organisation as Becca said.

Buying sick geckos from pet stores only validate their practices, and it gives them incentive to keep selling poorly cared for animals. It's sad and unfortunate, but you really don't want to give them money for it. If they are willing to give you the gecko for free because you want to rescue it, that's another story.

And as commented above, you can't put a small gecko in with a 2 year old full grown adult. Not to mention introducing a sickly gecko into the same tank where a healthy gecko is could potentially be deadly to your healthy gecko.

I would do two things, try your best to limp together a proper enclosure and then ask the pet store if you can take it off of them to nurse back to health.

If they say no, then report them. If they say yes, judge how much care it took to get it back to health to see if you should report them.

Some pet stores like the fact that they can unload sick animals to stop "wasting" resources on it.

Just because you don't think it isn't sick doesn't mean that it isn't. You would be risking Randall's health if you take another leo that MAY be sick and putting it in with him. In my opinion it would not be worth it, however it is your risk to take.