I’ve just created my own Blizzard account this past month, and at the same time, transferred 3 characters from my mom’s account to mine. At the time, she had access all the way to Dragonflight, and I believe she had also pre-paid for the War Within expansion. I, at the time as well, just had the base subscription. So I only had access up to Battle for Azeroth. I purchased the 3 character transfer on her account, and transferred my 3 characters with no issues at all. I tried to transfer 1 character from my uncle’s account this past week, who has access to Dragonflight only, he has not pre-paid for the War Within, and it won’t let me transfer from his account to mine. I created a ticket to see if someone could look into and see if there was a problem that maybe I wouldn’t know about, that was hindering me from completing the transfer. The response was that “you can’t transfer when you bought the item on another account. You will need to purchase it on your account or have someone gift it to you.” That response makes no sense, being that I did the same process I did with my uncle’s account, as I did on my mom’s, and doing from my mom to me worked, but from my uncle to me did not. Do I need to create another ticket and keep trying? Or is there really something I’m doing wrong. There was no clarity that I got from the ticket response. (I purchased just the Dragonflight expansion to see if maybe that was why the transfer from my uncle to me didn’t work, and that did not fix the problem.)
Great! Though there’s some troubling stuff I read below in the below quotes… Every adult should have their own account. If you’re a minor you can have a license under your guardian’s account or supervised by a parent but I don’t think transferring is allowed in the latter case. 
You shouldn’t do that… Those toons aren’t yours are they?
With gametime you have base Shadowlands, just not the latest expansion Dragonflight.
Transfers should only be possible between your own accounts and from equal expansion levels or towards higher expansion levels.
You should only be able to transfer between accounts when the names and information match! From your moms account sure if your account is in the same name and your a minor.
But there is no way to move anything from your uncles account to yours.
As Forumcat mentioned, you should not have been able to do the transfer from your mom’s account in the first place, being you were of lesser expansion level than her’s. Your uncle’s is working as designed.
If you just purchased DF prior to making this thread, it is possible that you may need to give it up to 24 hours to see if you’re able to transfer from his account. The pre-purchase could indeed be an obstacle.
Though I’m echoing Forumcat as well-- should you be? Are they your characters?
This part is fine. It was recently discussed in a similar thread where a parent wanted to set up a new Bnet account for their son instead of having them play on the parent account.
If he has characters on your account and you want to allow him to keep playing them, you’ll need to use the Character Transfer service. You should be able to gift him Character Transfer Tokens through the shop (they are currently on sale right now).
He’ll need one for each character he wants to transfer, so depending on how many that is, it might get expensive.
Assuming you share the same last name, and that is what he used to set up his Battle.net account, transferring characters from your WoW license to his should be easy enough. As Vorsol noted though, any Battle.net account bound item like mounts, heirlooms, appearances, toys, etc… will not transfer with the character so they will have to earn their own collection on their account.
If the names do not match, we may still be able to help but you’ll need to submit a Support ticket
You should only have been playing on the account of your parent though, not on your you uncle’s account. People can not give you characters.
That said, the transfer restrictions are listed here
Thank you all for your responses. I’m actually 25, and just moved into my own house, with a brand new computer I built, so I thought it was time to get my own Blizzard account. I guess I didn’t read well enough into character transfers and how they work. But yes, all the characters I’ve been referring to are 100% mine.
No, they are actually the owner of the battlenet account they originate on. Your uncle’s account means that all characters created on it are under his authority. You should never have been on your uncle’s account in the first place as account sharing is a bannable offense. As an adult, you should also not have been on your mother’s account. The only time account sharing is permitted is between an adult and one minor child they are parent or legal guardian of.