What are the approved sources for issuing fatwas, judging, and teaching in the four Madhhabs?

If the intent is to know the reliable fiqh books [books of subsidiary issues] for jurisprudence and fatwa in the four schools of thought, they are the same fiqh books relied upon in all other chapters of fiqh for each school.

As for the books specifically authored on the rulings of jurisprudence and fatwa, the most important ones are: - In Hanafi jurisprudence: Mu’in al-Hukkam by al-Tarabulsi, and Durar al-Hukkam by Ali Haydar. - In Maliki jurisprudence: Tabsira al-Hukkam by Ibn Farhun, and al-Itqan wal-Ihkam by Miyara. - In Shafi’i jurisprudence: Jawahir al-Uqud by al-Minhaji, and Adab al-Qadi by al-Mawardi. - In Hanbali jurisprudence: al-Turuq al-Hukmiyah and I’lam al-Muwaqqi’in by Ibn al-Qayyim.

As for the books specialized in fatwas: - In Hanafi fatwas: al-Fatawa al-Hindiyyah and Tanqih al-Fatawa al-Hamidiyyah. - In Maliki fatwas: Fath al-Ali al-Malik by Ibn Ulaish. - In Shafi’i fatwas: The fatwas of al-Ramli, al-Subki, and Ibn Hajar al-Haytami. - In Hanbali fatwas: The fatwas of Ibn Taymiyyah.