I am a regex specialist, but what you want is very advanced and would take some time to create and debug. If no one is willing to provide the solution for you here for free, you may think about hiring a specialist to do that. Sorry, I am not available for custom work but you may want to ask for it in the paid work forum.Help me please to collect my Regular Expression.
1. prohibit the CAPS (more than 2 letters consecutive), allowing the first capital letters, such as "Mary Doe" or "Catherine"
2. prohibit any special characters such as * @ $% _- and so on. like ö ä ü é à è Ö Ä Ü É À È too
3. prohibit all digits 0-9
4. prohibit more than 2 consecutive identical letters
5. prohibit consisting total less than 3 characters
6. prohibit the kind of nickname "Ad " that is, when nick begins or ends with a space
7. Allow all Cyrillic and Latin