As you see by other replies, getting guardianship is not always smooth sailing.
It does affect the relationship between a parent and an adult child, but my son has over time come to accept my assistance rather than resent it.
Videos of him laughing and talking will not help your case - simply being psychotic will not prove that he needs guardianship. You need to show proof that he is unable to manage his affairs, and cannot make decisions that will keep him and others safe. Keep records of those kinds of behaviors and solicit help from others who may have observed potentially harmful behavior.
My son had had multiple interactions with CIT officers over a 2 year period, who were able to describe behaviors and situations he had been in that could be a danger to himself. I requested assistance from concerned community members, such as clerks at the grocery store he went to, to provide written description of his behaviors there, emphasizing that they be very specific in how they felt the behaviors could be dangerous - such as speaking explosively to strangers, standing in the street yelling with cars going around him, or dashing in front of a bus. I also had the support of his psychiatrist, also with a letter describing him as gravely disabled. My son was already determined to be disabled by social security and was receiving SSI.
It all feels horrible. It is not what you want for your adult child. The last thing the judge asked me in the court hearing was, 'If your son’s condition improves to the point where he can manage his own affairs, would you give guardianship back?" My answer was, “I live and hope for that day!”