I see several people recommending quarantine.
Definitely read about quarantine and consider the matter.
But I would also consider whether it is worth the bother.
The point of quarantine is so you can identify any diseases or parasites the new chickens may have. Then you can either treat the problem before it spreads, or you can kill the new chickens to prevent the spread.
This makes sense when someone has a large existing flock, and is adding a few new chickens. It especially makes sense when the existing flock is very important (breeding, or personal attachment, etc.) and the person cares less about the new ones.
But with a total of only 3 chickens, I am not so sure. If the new chickens have something treatable, the worst scenario is that you have to treat all three of them-- not too much different than treating one or two. And if there is an untreatable problem, would you kill the bird with that problem, before it spreads? If not, then the problem is going to spread anyway.
So I think it is worth considering what you would do in each possible case (no problems, treatable problems, untreatable problems.) Then decide whether quarantine would make any difference.
Having chickens live alone is known to be bad for them. If you would not have any benefit from quarantine, it will be better to have the chickens together sooner. But if you WOULD get major benefits from quarantine, then it might be worth having the chickens live alone for that amount of time.
I am picking them up on Friday and would love all your tips for how to handle the new additions. I have never dewormed my chicken but have heard doing a round of dewormer when getting new flock members is a good idea? Do I do mite drops on everyone?
I do not know for sure about dewormer and mite drops, but those might be a good idea.
I suggest you give each new chicken a physical inspection before you ever leave the seller's place. If you find any major issues, do not buy the chicken and do not bring her home. Some of the articles have good ideas of what things to look for. If you find issues you are willing to treat, you can be making a plan to do that immediately, rather than giving them time to get worse.
I have a large dog crate but do not have a second coop for the newbies to chill in. How long do I have to keep them separate and will the two hens really be ok in a dog crate 24 hours a day? For how long? That sounds wild and not fun!
If you are trying to quarantine them, the new ones will need to stay in the dog crate (or perhaps in separate dog crates, if they come from different places and need quarantining from each other as well.)
During this time, the ones in quarantine need to be away from the existing one (and away from each other, if they came from different places.)
If you are quarantining, that situation could last for a month or so, or perhaps longer if you find some kinds of problems.
I have a large dog crate but do not have a second coop for the newbies to chill in. How long do I have to keep them separate and will the two hens really be ok in a dog crate 24 hours a day? For how long? That sounds wild and not fun!
Here is a pic of our current set up- there is a small coop inside the run, and we open the run in the am so she can free range in the yard a few hours, then put her in the run when we run errands etc- she's usually in the yard for at least 3 hours a day
After quarantine, or if you skip quarantine, you will want to have the chickens where they can see and interact but not yet be together enough to hurt each other. This is a look-no-touch introduction. This period often lasts for a week or two.
For this time, you can have the new ones hang out in the dog crate inside the run, but there are a few other options as well.
--When you let the current hen out to free range in the yard, you can let the new ones loose in the run.
--You could put the current hen in the dog crate, and put the two new ones in the coop & run.
--You could switch off who is in the dog crate.
All of those options can give some relief from being in the small space of the crate, and all of them let the new chickens start to become familiar with the coop & run without being bullied by the current hen (or bullying her.) You do not have to pick just one, but can mix and match who is where at what time, in any way that seems like it will work.
Later, after the new chickens have been with you long enough to know this is "home," you can also let the new ones have a turn free ranging in the backyard.
At some point you will let them all be together, and watch what happens. Sometimes there are big fights and you have to break it up, sometimes one or another will act like bullies and one will be chased into a corner, sometimes everything will go smoothly. Depending on what you see, either they get more look-no-touch time, or they are fine, or you ask for more advice and change something.