Remember folks, the Marvel agreement in Orlando has been updated and we don't know the contents of the most recent agreement.
Not to mention the original agreement was super vague. For example what is a 'family'? In the Marvel universe almost every single character of note did a stint with the Avengers, which would mean Universal has a lock on all Marvel characters. But the contract makes clear that that isn't the case.
Vague.
Also, as mentioned above, Shuri has taken the mantle of The Black Panther. But Shuri's Black Panther isn't an Avenger.
And because Black Panther was an Avenger doesn't necessarily mean his 'family' is off the table. It's the Avenger's family that's off the table.
But this rumination is all based on the vagaries original contract which is now superseded by a newer one that we haven't seen.
And it would be odd for Disney to be thinking about Wakanda for Epcot for the past five or so years if they weren't allowed to do it.