What is the best way to ensure that the system forces the capitalization of name and surname?
A JavaScript in the validation.
See: examples in https://stackoverflow.com/questions/196972/convert-string-to-title-case-with-javascript/196991
What about a Xpress Policy on (before) CreateUserEvent and ModifyUserEvent?
You can try an Xpress Policy of type = UI. In the data element use category = general, type = string parser, function = to Upper.