Where is the world's largest palace that is still the normal residence of its country's royal family?

The largest royal palace still lived in by a royal family is Windsor Castle in Berkshire, UK.

"Windsor Castle is the oldest and largest occupied castle in the world."

https://www.rct.uk/visit/windsor-castle

Brunei. Istana Nurul Iman, is the worlds largest functioning residential palace.

The world's largest residential palace is the Istana Nurul Iman, near Bandar Seri Begawan, capital of Brunei. Official home of the 29th Sultan of Brunei, Hassanal Bolkiah, and also the seat of the Brunei government, the palace covers 200,000 m² (2,152,782 ft²) and contains 1,788 rooms. It also has 257 bathrooms, banqueting hall for 5,000 guests, large mosque, garage for 110 cars, air-conditioned stable for 200 polo ponies and five swimming pools. Designed by architect Leandro V. Locsin (Philippines), with interior designs by Khuan Chew (UK), the palace was constructed by Ayala Corporation and completed in 1984 at a total cost of around $1.4 billion.

https://www.guinnessworldrecords.com/world-records/largest-residential-palace

The Istana Nurul Iman in Brunei holds the title of the world's largest functioning residential palace. The Istana Nurul Iman in Brunei isn't just a palace-it's a living, breathing royal home. It's massive, with nearly 1,800 rooms and space for everything from luxury car fleets to polo ponies, and it even has a mosque and banquet hall that can host thousands. What makes it special isn't just the size. It's that the Sultan actually lives there, making it the largest royal residence in the world still used as a full-time home by a ruling monarch.
https://en.m.wikipedia.org/wiki/List_of_largest_palaces