Please provide a definition of the legal concepts "compliance", "regulation", "enforcement", "law firms in Malta", "immigration by investment", "challenges", "regulatory authorities", "legal obligations" and provide references to literature used. Specify the EU legal framework that impacts immigration by investment: EU directives, regulations, and policies that influence or set the parameters for immigration-related practices. Provide ethical considerations. Explore how law firms identify, assess, and mitigate risks associated with compliance.