THIS IS NOT LEGAL ADVICE.
If you want an answer to rely on, your brother should hire a criminal attorney in Orlando. That is the only way to ensure he is getting correct information.
But if it were me, what I would do is first look to see who issued it. Was it Universal itself, OCSO, or Orlando PD? He caould call them, but I wouldn't expect any legal advise to be given.
Then I would look to see any statute referenced in the written warning and then read the statute. Amazing what you learn when you actually read the law!

Then if I still had questions, I would use google. For instance, I found the OPD trespass procedure document that outlines requirements and protocol for criminal trespass.
https://www.orlando.gov/files/share...rnings-and-trespass-authorization-forms-2.pdf
Pay attention to 4.2.1 It may help you, but only if the issuing agency is OPD.
Again, I cannot stress to you enough that the proper way to handle this is to hire an attorney to look into this or just not go. It's expensive, but not as expensive as defending a criminal case.
Also, service and receipt of the warning may be an issue here. How did he get the warning and how did they know he received it? This is a very valid defense but he doesn't ever want to be in a position to have to rely on a defense.
Good Luck!